I think you can get 10lbs of the ON 100% at advantagesupplements.com for around $52. It comes in 2 5lb bottles. Seems like a pretty good deal to me, retails at GNC for $95ish
Actually, it used to be cheaper. ON has raised its price, I think. www.allthewhey.com has some really good specials. I think you can get 10 pounds of a whey blend for less than $40.