About 30,000. I didn't use any glitches and didn't get the fortune finder perk.
Basically, I played a ridiculous number of hours in the game, but really, by about 20 hours in, if you boost repair and medicine to the top, have a favorite set of weapons you always use and don't constantly change your house around, you have more caps that you can use. It takes some work, because you have to be find people who will still have caps to trade for your crap, but you can do it.
Ammo is a great way to get tons of caps. I never used the 5mm or 10mm ammo, sold all of it. I never used rocket launchers, so sold any rockets I picked up. Sold all rail spikes, darts, flamethrower fuel, BBs and .32 rounds as I never used weapons that used that ammo.
Ammo is worth way more caps than any of the wasteland detritus you can pick up, and it weighs nothing, so it's easy to build up caps that way. I didn't even have to get the ammo perk.