I'm looking for a developer that has already built a collective buying site or has experience in sites that have similar functionality.

Below is a description of the applications the site will need to be able to perform, but to keep the specs simple, please visit the following two sites below.  I am looking for a virtual mock version of these sites and all of their functionality.  The user interface can be different, but the functionality must be, at a minimum, similar.

http://www.groupon.com
http://www.buywithme.com