Yeah, I noticed that also and spent all my money, but still for some reason I left the magnum ammo until last just in caseThe last time you meet Duke he hints that maybe you should spend that money! Hinting that you are near the end.
I upgraded, crafted everything etc at that point and used my magnum and nade launcher as I knew we were nearing the end and didn't need to be as careful with ammo.
Bloody hell, you missed a lot. I felt the game did a good job showing which items were combinable. I found and combined everything and made loads of cash.Just found a couple of 'secret' areas with lots of stuff and also learnt that treasures can be combined to make them more valuable not that I really need the cash.