Depends what kind of friend he is, how fair he's treated you in the past, and how much difference in price. I know one guy who every time he meets someone new that sells he starts buying from him and goes back and forth trying to get cheaper prices by saying I can get it from Joe Blow for this price. Now that everyone has figured him out everyone has cut him off. Not saying it's the same here but there is something to be said about loyal customers, friends or not. If it were me I would just tell your friend what's up, tell him you would rather stay with him but you would feel bad paying more than you had to and can he at least match the price.