^ What he said.
Bubble wrap them, then shrink wrap them, and just drop them off at Greyhound. Assuming the buyer has a terminal near them, it shouldn't be a problem.
I've gotten large exterior parts this way for cheap (i.e- set of 18" tires from Oregon for $50, stock front bumper from New York for $30, etc.).
Your other option would be to ship it freight. Assuming you are a near a major airport, you could find a company such as Forward Air, and they will charge you by the pallet. That's how I shipped my old Getrag to get rebuilt. It was like $90 for the ~150lb pallet.
But again, the next dilemma with that is that the buyer has to have a location near them.
http://www.forwardair.com/locations/falocations.htm
^I'm in no way affiliated with them, but I've just used them in the past to ship heavy freight.