Don't you wish you had one of these to sell...

An operational Apple-1 will go on the auction block later this month, and the rare computer is expected to fetch as much as $392,000.

The 37-year-old machine -- thought to be one of only six in working condition -- is expected to sell for between $261,000 and $392,000 at the current exchange rate, according to German auctioneer Breker, which is conducting the sale. As impressive as that range may sound, it's far off the record mark of $640,000 set last December for Apple's first production computer.

Constructed in 1976, the Apple-1 is one of only 200 produced. British auction house Sotheby's estimates that only 50 still exist.

In a time when most personal computers were sold as self-assembly kits, the Apple-1 broke new ground as the first personal computer sold with a fully assembled motherboard. However, at a retail price of $666.66, the Apple-1 didn't include a casing, power supply, keyboard, or monitor. A cassette storage option could be purchased for an additional $72.

The lot up for auction on May 25 includes the original owner's manual as well as a letter signed by Steve Jobs to original owner Fred Hatfield in which the late Apple co-founder offers to exchange the Apple-1 for an Apple 4K II for an additional $400. The back of the circuit board also bears the "Woz" mark of Apple co-founder Steve Wozniak, who built the Apple-1 in Jobs' parents' garage.

Early Apple machines have become a recent favorite among vintage computer collectors. While Breker sold another Apple-1 last December for a record $640,000, another Apple-1 sold for $374,500 at Sotheby's last June.