Got some good ammo/money tips from some nice fellows at gaf:
Sometimes outside Megaton, there's a trader. He's got a Brahmin caravan and there's always someone out there to help him protect the merchandise. Kill the trader, then kill his guard. Loot everything they've got. You will get a key on the trader that allows you to get to his supplies. Take everything. Sell all the crap you don't need, repair dud weapons with the loot you get from the pile to make them stronger. You won't have ammo problem if you're doing that.
If you're rolling good guy like I am, you can balance this evil act by giving the dude nearby, Micky, some purified water, which is a good act obviously. It balances it out this way so you don't get too bad. You can get purified water from the robot in your house.
Anyways, I've been selling all the misc. crap I don't need on my trips, and I went from zero caps to about 1200 today's playthrough.
I made it to Rivet City (?), went to Vault 112.
This is goty. Only thing that will come close is Persona 4.