Whats your Budget ??
Depends on the script.
Max use will be 0.20 BTC Depending on the script, and the functions it offers.
Trust me, you don't want the dice site people are willing to sell for 0.2. It will most likely be an outdated version of
https://bitcointalk.org/index.php?topic=507515.0 - Filled with exploits and backdoors. I highly recommend staying away from ANYONE offering this script besides johny1976 but that's out of your price range. There is still a good chance someone will exploit your site even if you buy from the original owner since the code is shared by many.
Free:
https://github.com/felinegambler/CryptoDice - but again there are exploits. One can be seen here:
https://bitcointalk.org/index.php?topic=909282.0Hmm...
Well, I do have someone who is able to check the script..
But it sounds like just about anything can and will be exploited :/