U guys must already know about Item regenerating trick, but try doing it in chapter 3-1. Each run will give you at least 13000, not counting the Gold Eggs u might find. But remember not to take those plates to open gate or u'll make enemies come out and make the looting process much harder. And if u looking for a specific type of ammo, try equiping that weapon with NO extra ammo with you, you'll likely find more of that ammo. Works well with shot gun, rifle and machine guns. 
