I have a line on a 58 commando. It is in pretty rough shape. missing a head light and ring. as well as having a bobbed rear fender. Looks like the bike is reasonably complete though. It has been stored in a dry barn but not protected in any other way. My question is how much should I offer for this bike. I am sure this in speculative and difficult given the sparse info I have provided... But I don't know where to start in a resonable negotion with the seller. They have simply said "make an offer." Thanks...