Apple owners know that the company's latest computers cost a pretty penny (or more accurately, hundreds of thousands of pretty pennies). But how much is one of their oldest computers worth? Judging by the opening bid at Christie's, at least $300,000.

One of the original Apple-1 computers, Apple's first foray into computing, is now up for sale. This particular computer originally belonged to Ted Perry, a retired school psychologist living in California.

When the computer was first released back in July 1976, it retailed for $666.66 and did not include a monitor or other key components. Only about 200 other Apple 1 machines were manufactured, as less than a year later, the company released the Apple II and encouraged customers to upgrade.

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According to a Christie's specialist, this particular Apple 1 appears to be among the first 25 computers to be produced. "It does not have a diamond NTI logo (the PCB manufacturer) etched into the front copper layer," the specialist notes. In addition, the working machine up for sale is labeled with the serial number 01-0025, and is signed by Steve Wozniak. It's estimated to fetch as much as $500,000 at auction.

In May one of the Apple-1 computers sold for $671,400 (516,461 euros) at an auction in Germany. Earlier this year, one of the same types of computers didn't manage to hit the $80,000 minimum at Christie's; however that model no longer works.

The auction itself is an online exclusive and ends July 9. Also up for auction are several other Apple antiquities, including floppy discs containing the company's first word processing and spreadsheet programs, as well as a prototype portable computer several times thicker than today's Macbook.