you can get a 72 watt tec from becooling.safeshopper.com for $15.00. it comes with a power connector, but the tec is not potted(waterproof). dangerden has a 80 watt tec that is potted but its $24.00.
what size psu do you have? you can get away with using your computers psu if its 300 watts+ to run one tec this size. you wont get the best performance, but it will still work rather well.
also make sure to insulate gpu (front and back) so no air can get in there or else you will get condenstaion, and thats not good.
you can find some great info on this web site under peltiers, also procooling.com(look at the pelt fourm), and tedist.com have lots of info.
hope this helps.