If I am reading the fee schedule right, $75 is the max charge for a 100 pound "item" with a max L+W+H dimension of 80" inches. UPS would charge me (with special rates) $122 and take 7 days (at best) NYC to SEA , I'm sure the public rate is much higher, near $150.

"Media Mail" rate is what you have to ask for at the post office or USPS.com for items like printed books, magazines and software. For whatever reason it is sorted through separate special facilities and takes much longer (double+) than normal priority mail, perhaps because they reserve the right to open and inspect the packages.

Shipping has become my life...

LATE EDIT: Only applies to the first 2 bags checked in otherwise $150 per bag