Insane prices arent limited to ebay. Look at some consignment shops, ive seen ibm xt machines with 300 dollar price tags, c64s with similar prices.
I think people often put stuff up for sale, not knowing what stuff is worth, so they just set the price high. You often see 15 year old tv's complete with color problems and bleed in for 200 bucks. VCRs for 100 bucks, and beat up couches for same price.
Go check out a pawn shop, and see what they want for computers. Insanity. I saw a pawn shop the other day that had a compaq tower, with like 8 bays ( proliant machine i think). It was a 100Mhz machine with nt4 installed, they wanted 900 dollars, i tried to negotiate them down to 20 dollars, they laughed and told me it was a "server".