I shipped a 125lb A555 transaxle from a Chrysler from California to Connecticut for $62 through FedEx. IIRC, the maximum weight they will allow is 150lbs... so if the MTX-75 is under 130 or so lbs, you are good to go. Don't forget that the packaging to support it also weighs quite a bit.
To package it, I bought a big box, and used my table saw to cut some cheap particle-board to reinforce the cardboard box.. then I filled it tight with newspaper. Quite a process, but I think the packaging added up to 20 lbs. A non-reinforced box will turn to mush with that much weight pushing at it.
Ah Ebay....