I ordered 8 lbs of varying powders from PF.com about a month ago. Shipping is a little steep and they aren't the fastest to get their product out of the door, but the price per lb can't be beat. Just make sure to order a substantial amount to make the shipping cost worthwhile.
I must, however, use a blender with all of their powders. Store-bought powders would usually mix with a spoon, but not these bad boys. Maybe that means the store-bought stuff had added emulsifiers, I dunno.
The taste is also pretty harsh, so if you're ordering from them, make sure you into BB as a discipline and not just for a fling.