Kiva.org Style Site

I'm putting a feeler out there to see how much a website like this would take to script. I don't need a design, just a backend. Basically I want a site where people can post a cash prize and have other people try to do what that person wants for the prize. The winner is determined by whoever payed the cash prize. Again, this is just to see the development costs, if you can do it within my price range and fairly quickly, I'll probably just pick you to do it :) Thanks!