Is Royal Wedding Under Cost Constraints?

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WATCH Will and Kate's Wedding: Who Foots the Bill?

Prince William and Kate Middleton's wedding is expected to be one of the biggest events of 2011, but it will not be a time of blind spending for the king- and queen-to-be, according to a royal expert.

"There are constraints involved," former Buckingham palace spokesman Dickie Arbiter told "Good Morning America." "William and Kate are going to be aware they're under the microscope in terms of costs."

Prince Charles announced the engagement of his son Prince William to long-time girlfriend Kate Middleton early Tuesday, sending the entire British nation and an international media into a wedding-warped frenzy as to where and when the wedding will be held, and what it will cost.

But the island nation has been reeling from the global economic downturn and recently slashed $130 billion in spending, and half a million public sector jobs, focusing special atttention on what the royal blowout might cost, and who will pay for it.

Estimates for the ceremony's price tag range wildly -- from around $20 million to $75 million.

"There are all sorts of figures being banded about. Someone was talking about 30 million pounds 30 years ago for the wedding of Charles and Diana. It was nowhere near that, and it won't reach that sort of figure now," Arbiter said.

William's father, Prince Charles, is expected to pick up most of the check for the wedding, including a possible donation from the queen. But security costs, which have been estimated well into the millions of pounds, will be paid by police and government agencies, Arbiter said.

But the wedding is also expected to give a helpful boost to England's economy, reportedly bringing in as much as 620 million pounds in the form of tourism and consumer spending, according to one retail researcher.

Middleton Photographed at Westminister Abbey

As to where the wedding will be held, rumors that the happy couple could say their vows in Westminster Abbey gained traction Wednesday when The Daily Mail snapped pictures of the bride-to-be leaving the historic church.

Arbiter said the abbey would make a logical place for the wedding due to its proximity to Buckingham palace.

"Westminster is a good option. ... It's good for planning security, good for a carriage ride," he said.

It would also make for an emotional return to Westminster. It was the same place he said his final goodbyes to his mother, the late Princess Diana, at her funeral in 1997.

According to Arbiter, the abbey can hold nearly 3,000 guests, but it could still be months before the much-anticipated guest list is made public.

"What you've got to remember is that you've got guests William and Kate want to invite, there are guests that William and Kate have got to invite because there's the commonwealth aspect, there are world leaders that have to be considered, there are friends there are family. So they're already thinking about that," he said.

After much speculation about the timing of the wedding, today rumors are swirling that March could be magic month, Arbiter said.

"There's a lot of speculation that it's going to be a summer wedding, but I think it's very telling in the announcement that the palace put out yesterday that it could be a spring wedding," royal expert Katie Nicholl told "GMA" Tuesday. "And royal engagement announcements by tradition are short. So I wouldn't rule out seeing something perhaps as early as March or April.

"And June is the month that's being batted around because it's the month that Prince William turns 29. ... That birthday date could be very significant," Nicholl added.

Within hours of the announcement, and Middleton's appearance wearing the late Princess Diana's famous sapphire-and-diamond engagement ring, orders for replicas exploded, crashing jewelry websites.

Tuesday's announcement was followed by visible sighs of relief from the happy couple, and the queen said she is "absolutely delighted" for the couple, Buckingham Palace said hours after the announcement.

Like the queen, Middletons' parents, Michael and Carole Middleton, said Tuesday they too were "absolutely delighted."

'It's About Time.' Royal Engagement Announced

Eight years after the couple met, Prince William appeared with Middleton for the first time as an engaged couple Tuesday.

"The Prince of Wales is delighted to announce the engagement of Prince William to Miss Catherine Middleton," a statement from Clarence House early Tuesday read.

Prince William, 28, asked Middleton, also 28, to marry him while the two were on vacation in Kenya last month, the statement said.

The happy couple appeared for the first time for reporters arm-in-arm before a barrage of camera flashes, Middleton wearing the famous engagement ring worn by William's mother, the late Princess Diana.

"He's a true romantic and we had a wonderful holiday in Africa and it was out there in a very quiet lodge and it was very romantic and it was very personal time for both of us," Middleton said.

In an interview with Britain's ITV News' Tom Bradby, who told "GMA" the interview was "terrifying," Middleton said the proposal came as a surprise, despite years of public speculation that the couple would wed.

"We were out there with friends, so I really didn't expect it at all," Middleton said. "It was a total shock when it came. Very excited."

The announcement came to the elation of Britons, many of whom viewed the engagement as a seemingly inevitable yet unreachable moment. Within 25 minutes of the announcement's posting on the royal Facebook page, more than 1,400 people "liked" the news. The numbers have since increased.

"It's about time! Congrats," one commenter wrote, a sentiment echoed by hundreds of others.

The Long Courtship

The two met nearly a decade ago while students at the University of St. Andrews in Scotland. The relationship garnered some controversy because Middleton does not come from royalty and royals are generally expected to wed other aristocrats.

William said the two were friends for more than a year and lived as flatmates. "It blossomed from then on," he said. "We had lots of fun. ... Same interests. She has a really naughty sense of humor."

When asked why it took so long to propose, a beaming William quipped, "I also didn't realize it was a race, otherwise I probably would've been a lot quicker.

"We have a great fun time together," the prince told reporters. As for the ring, William said, it, like Kate, was very special to him.

"Well as you may recognize now, it's my mother's engagement ring and it's very special to me, as Kate is very special to me now as well. It was only right the two were put together," William said. "It was my way of making sure mother didn't miss out on today and the excitement and the fact that we're going to spend the rest of our lives together."

Diana received the ring from Prince Charles after the two were engaged in 1981. At the time, the sapphire ring, which is surrounded by 14 diamonds, cost 30,000 pounds, or about $47,500 at today's conversion rate.

"I had been carrying it around in my rucksack for about three weeks before [the proposal]," William told ITV. "Everywhere I went, I was keeping ahold of it, cause I knew if this thing disappeared, I'd be in a lot of trouble."

"It's beautiful," Middleton said, as she showed the ring to ITV's camera.

While Middleton is now wearing Diana's ring, William said, she won't be in his mother's shadow.

"There's no pressure," he said. "Like Kate said, it is about carving your own future. No one is trying to fill my mother's shoes. What she did was fantastic. It's about making your own future and your own destiny, and Kate will do a very good job of that."

William said he didn't know where to start when asked why the couple was apparently so loving, but said she makes him laugh. For her part, Kate said William was very supportive of her.

William and Kate broke up briefly in 2007 but were back together within months.

Prince William is second in line for the throne, after his father Charles, Prince of Wales. Prince William's mother was Diana, Princess of Wales, who died in an auto accident in 1997.

The royal couple plan to live in north Wales, where Prince William will continue his service in the Royal Air Force, the statement said.

ABC News' Nick Watt, Sarah Netter, Jason Volack and Bradley Blackburn contributed to this report.