If you want easy money in game, you can use the infinite Sydney's sub machine gun trick (might have been fixed in a patch). You need to have beaten the quest where you find the thing for Abraham Washington, (the name of the Item and quest escape me at the moment), but if she survived and you got a holo-disc from the Hotel (The one involved in the Reilly's Rangers Rescue quest) It on a nightstand on like the second floor. Anyway if you run into her either in Rivet City or later Underworld. If you let her listen she'll give you the gun, ask her about her father let her here the tape, she'll give you the gun again, repeat until satisfied, I managed to get 400 caps per gun