We want similar system as freelancer.com for rewards build in our website.
The website is build with smarty framework, so before bidding make sure you understand smarty but also first have a good look at the script wiiki for building add-on in it.
http://tinyurl.com/caz8xn6 is the developers section, where they explain how to build add-on
The rewards module must be build as add-on, so that it possible to turn irt off , or update the module seperatly.
The website is our base , and we look for a skilled programmer to do several tasks on that domain on a regularly base.