Be careful of a good deal. While most are on the level sometimes it's only a good deal for the seller. You can buy a revolver for a hundred bucks, only problem is you may wind up with a hundred dollar paperweight.
Go to a gun store, hold a few, find what feels comfortable, if your friend wants to sell you his gun get a box of ammo, bring it to a range and put a few dozen rounds through it.
People do more research and testing when buying a car and that just brings you from point "a" to point "b". Why cut corners to save $20 when it comes to a gun?