Don't even waste your money upgrading any guns other than to get the Dillinger and the Streetsweeper. The Level 1 pistol will kill your enemies with one headshot anyways. Once you get those two guns, you have like 600 rounds to use between the two, so you never have to use any other gun. I would use the money to buy safehouses, so its easier to rob banks and you can get your free ammo.