Reliable-PROVEN Groupon like script

We are starting a group buying coupon site like Groupon and wanted to see if anyone could give us a referral where to find a reliable-PROVEN Groupon like script. If possible we would like to take an existing script and modify it to meet our needs. We need a script that that is currently in use with at least 2-3 active – English URL’s (active- pending deals and transaction history). We need to be able to validate the usefulness of the script to complete our due diligence. Thanks in advance. is quite good but also expensive. I recommend this because for me it is proven ( think also that they where the first on this market ).
I saw on forums even free gorupon clone for wordpress or with limited features.
Also with a budget less then 100$ you can get a good groupon clone with all kind of features.