Shipping with greyhound is your best bet.
When I shipped my recaros to California I went to walmart around the time of night they were restocking shelves and had them give me the box that held their largest rubber maid tote.
I took the backs off the seats and arranged them to fit. Wrapped the whole thing in gorilla tape $$$ and had my girlfriend take it to the greyhound station.....
(Some how she lifted it onto the top of her chevy corsica and tied it with hair ribbons or something and made the 2 mile trip to the grey hound station where she somehow unloaded it and got it shipped... for like $80. She is about 100# soaking wet and claims she fell off the roof of the car three times in the process. I am still super impressed.)
So yeah... $80. GreyHound is awesome.
Sent from Outer Space!