If he/she is a friend, then it really doesn't matter how much it costs right? Or just tell him/her how much you can afford and see if your price can be matched. I thinking reasonable condition FM2 and 50mm lens should cost about $600-650.
But if you are thinking of starting from scratch and basic, and if you don't really need to buy from your friend, then I would really recommend either buying two prime lenses such as 35mm wide and a 85mm or 105mm short tele as a start. Forget the 50mm as a starting lens because you are really limited in what you can do. Or you can get get a standard range zoom, eg, 28-85, that should be good too.