If you're looking to spend less than 4.00 per lb,you are not going to be getting a high quality Whey(like an Isolate form),but rather a cheap concentrate form.Any time you're getting whey for under 6-7.00 per lb.,quality of the compound is in question IMO.
Bump for Optimum Whey 100%, can get a ten pund bag for around 40 bucks if you shop around. Great protein profile w/ extra good content, works for me. Or you can try AST VP2 Whey Isolate, expensive, but from what I hear is excellent stuff.
I picked up a bag of pure whey from nutrabiotics for around 3.50 a pound. It comes in 33 pound bags and it was $80 + 30 shipping. The protein is flavorless and has mixed very well into different shakes and homemade bars. Not a bad option along with the motivation of using it all up as to not waste your money.