insane, how many of those are in junkyards?
Practically all of them. When the Apple II came out, Steve Jobs allowed a trade-up and junked all those turned in. A couple associates begged to keep a couple, otherwise there would be fewer than four working ones. Jobs did not like old clutter sitting around, and when he returned to Apple in the mid-90's he forced them to dump all their non-current inventory including museum-type stuff the company had kept. Fortunately, some was given to Stanford U. Jobs hated old stuff.
Be careful buying old stuff, there are scams out there.
“insane, how many of those are in junkyards?”
Very few. Only 200 were ever made. The Apple I was the first single-board computer ever made, including BIOS and all onboard I/O controllers. Steve Wozniack invented both the single-board computer and BIOS. In terms of the history of computers, his feat is akin to what the Wright brothers did and owning one an original Apple I board (only six left in the world) would be like owning an original Wright brothers airplane.
Not many. The reason these are rare is that Apple offered an aggressive trade in program program when they released the Apple II: turn in your Apple I board and get a free Apple II and $400! Most people who owned the 200 or so Apple Is that were sold accepted this generous offer. The owner of this one turned down the offer and that letter from Steve Jobs making the offer is included in the sale. Their was method in this madness. Wozniak was handling warranty service on the Apple Is at the same time as he was working on designing peripherals and other things for the Apple II. Warranty work was not a good use of his time.