This would be cool mixed with kind of a flipped free shipping thing, where I pay USPS $x a year and they deliver me up to y packages a week/year/whatever with n

This would be cool mixed with kind of a flipped free shipping thing, where I pay USPS $x a year and they deliver me up to y packages a week/year/whatever with no additional charge. You give the reference number to the vendor, the shipping comes up as free, they print a label and ship.