I built my own using an ardino clone and a couple of shift registers to provide enough i/o pins. It probably cost less than £5 in parts, offset by 5 or more hours designing and fabricating the thing.
But if you're looking to build a 6502 single board computer, it's actually a great preparatory project!
I should share the schematics and code, but I'd have to spend some time polishing them for publication - I built it on a breadboard, so I'm not even sure if the schematic is accurate.
