Its an almost impossible thing to put an accurate price on, you'll get some on here saying about £300 a side, up to many thousands for a proper job...
So my best advice would be to find someone you can trust, and then discuss a budget with them, but be prepared for any budget to go straight out the window, after a few weeks work! Falling out over a blown budget is very common, so a good relationship between yourself, and the Bodyshop is imperative
Contact local clubs in your area, and see who's recommended... certain names will keep popping up

Thom