Hey Chris.

When I go to the P/O in Detroit, their 2 smallest size boxes (bigger one will fit a dozen smokes fairly easy) are free and I believe both sizes cost $4.55 to mail (inc DC #). I agree with what someone else said, maybe you're looking at the flat-rate ones where (I believe) whatever you can stuff in 'em, regardless of weight, costs $8.10, no matter what.