Ok, it depends on what you're looking for, as far as taste and how much you want. Since by bang I assume muscel growing properties I will assume you don't care about taste.
If taste doesn't matter you should get natural whey powder, which is just a cream colored powder that tastes like bland milk when dissolved. You can get an 11 lb. bag for $42 or a 33 lb. bag for like $120. By far the best deal from any sports supplement company.
If you really feel like going all out you can find a dairy or milk processing company. One that members have used before is American Cesein. You can get the same stuff in 50 lb bags for less than $3 a lb. They also sell instantized casein in similar quantities.
So there you have it, the best bang for your buck in whey proteins.
JC