I guess it depends on what lens it is. If it is something commonly available on the used market and not too expensive, I would just buy another one in better condition. The bent one could be sold on eBay, with the ding clearly disclosed and photographed. If, on the other hand, it is an uncommon or expensive lens, then certainly I'd send it to a reputable shop to be repaired. The repairman will disassemble the lens, clean it and put it back together with the bent parts replaced by new parts (or used parts in excellent condition). I'd call around before just sending it blindly to a shop tho.
I'd never attempt to repair a bent filter ring by bending it back....either its worth getting done right or it isn't. If its not worth getting done right....just buy another. I might, however, venture to disassemble the lens myself to see if I could replace the bent parts....just to learn something.