I never thought much of any so called special edition stuff. As far as collecting value goes, if it's been shot and has wear the collector value is shot as well. Additionally, when is a Ruger LC9 going to have any collector value?
If I were you I would pass on his and get a normal used one for $300. Shoot, I'd sell you mine for that if you were local.
If giving him the extra $50 means you feel better about your friendship then go for it. I don't do any special deals with friends anymore. A "friend" at work talked me down $30 on a red dot that he turned around and listed on BackPage for $30 over my original asking price. That clown was trying to make $60 on our "friendship". Then he wouldn't budge on a flashlight I was interested in. I stopped talking to him after that...