You can buy keys off of keyvendor.com, for ~69% US price (71% for EUR price, which is equiv to 2.43 USD). Even greater savings if you are in state with income tax (they cost me $2.71 each), since Valve charges US sales tax.  They like to subsidize EU country, like Sweden and 25% VAT.

They are $1.72/ea there.

Why not just use this?