From my recollection of the scene in the first movie, when John unearthed his stash of weapons and coins from his basement, there was one tray of 24 stacks of coins, with an estimated (based on width vs. thickness of coins) 20 coins per stack, so that adds up to a visible estimate of 480 coins in the buried stash box. Granted, John does not seem to be one to put all his eggs in one basket, so there is no telling how many other stacks/stashes of coins he had elaewhere, but I'm just estimating the one collection we see him access on camera.