Psp Game Codes

I am looking to purchaseGod Of War: Ghost Of Sparta [Online Game Code]. I just get a little discuraged when I can go to the other stores and its $19.99 but when I go to Amazon or gamestop its $39.99. Does anyone else know if the game is cheaper somewhere else? As a reminder I have a PSP Go. Ty

I just found it on the PSN for $29.99! Just to be $10 cheaper then I am golden :D