I can fit at least 2 and MAYBE all 3 into a Priority Mail Flat Rate envelope. They ship for $5.15 ea envelope. The post office is getting pretty fussy about how much you stuff into those envelopes so I'm not sure if I can get away with putting all 3 into one envelope or not. When it comes to shipping heavy items like books it is often cheaper to go with Priority Mail flat rate packaging than by "regular" mail. I would say worst case scenario you'd be looking at $10 (because I've quoted $5/book and know for sure that I can ship 2 together). Priority Mail is the same price no matter where you ship in the continental US