Who knows what kind of damage you have already done. Don't make it worse. The price will depend if that is they only have to reinstall the spring, probably less than $200. If you have other damage, the sky is the limit, unfortunately. Hopefully, that is not your case.
The way the trucks secure the vehicles to the platforms are very crude. Usually they use chains attached to different parts of the car, like the drive train (HINT), to secure them. If it was attached to the wrong place...well damage will ocurr.
Sorry about your mishap!