If you want the gun, then get it. The few hundred dollars will be forgotten about eventually, but the gun will give you years of pleasure. Or, you could "split the difference" between your offer and his asking price.
There are some guns I purchased in past years that I know I overpaid for, but I have long since forgotten what I paid but still have the gun. (More than likely they are now worth more than what I overpaid for them.)