Having a starting price in the $10k range also weeds him out. In my market (Austin), if I have $10k for a prototype (even half that) I can throw a cat and hit a Ruby guy, a Python guy, a PHP guy, etc. The price as he has it is low enough that people with "an idea" might take the plunge to get a prototype going.

If I were to have one suggestion it would be for his site to spell out some parameters about what a prototype is so there are no later arguments.