Digikey sells an Intel chip, P80C3224SF88, which is a ROMless 40 pin DIP for $4.40 in single part quantities. At 500 parts the column pricing is down to $1.595 or $797.50 per 500.

Of course, this is a retail price for a currently available chip. I would recommend offering them on eBay, in a dutch auction, with an opening bid of $1.00 to $1.25 and let the market dictate their value. This also allows you to let the buyers determine how many they want.