These are all PC games:
Halo 2 - $19.90
http://www.gogamer.com/Halo-2-DVD-Rom--I--Front-Page_stcVVproductId19473615VVcatId444710VVviewprod.htm
Halo 1 - $7.90
http://www.gogamer.com/Halo--Combat-Evolved-Front-Page_stcVVproductId4760061VVcatId444710VVviewprod.htm
Hitman: Blood Money - $7.90...
The cheapest I can find one is $20 at walmart or target. I was hoping to use a GGC at Best Buy, but the regular price is $25 there. I don't think they will price match and use the GGC.