"It's exclusivity. People can't just go do it," Sheard said. "It's mind-blowing what you can see down there. The places you have the possibility of going are literally where no man has been before."
Not everyone agrees that the crafts are the new plaything of choice for the rich and famous.
"There's been an increase in the interest of submarines generated by those interested in increasing that interest," Stockton Rush, co-founder and CEO of OceanGate, told ABCNews.com. OceanGate organizes underwater expeditions, mostly for research purposes.
"It doesn't take much to double sales," Rush said, when only a handful of subs are sold each year.
Rush also pointed out that boat and submarine combinations can be tricky, as they require special attention.
Subs require specialized training, dedicated space on the boat due to their bulkiness and weight and special certification to travel to certain places.
"There's definitely an interest in undersea exploration and in submarines in general, but the interest is in going underwater and seeing stuff, not in owning submarines," Rush said.
Rush doesn't deny the draw of the dive, which he calls a "spiritual experience" where passengers see and hear things differently than they ever have before.
"All the sensory input you get, plus the emotional side…it's totally indescribable," he said. "Everyone gets passionate about the experience."
And for those who happen to be both passionate and wealthy, a submarine may be just the thing they're looking for.