Believe it or not, Amtrak is a pretty cheap way to move your stuff if you don't have access to a cross country rental van.
I guess they need to make revenue from all that empty space underneath the passenger area.
Simply palletize your stuff, within their weight & height limits, and drop them off.
You'll need to be close enough to a train station to get your stuff there, obvs.
Granted, it was a while ago, but I moved my whole 1 bdrm. apt. this way once for about $90, not including transpo on either end.
Might/could be worth a phone call if'n you've got some hot Amtrak action up in your zone.