That's a general problem in the Fallout games as well as many others. Economy usually works just a few levels and then it breaks. In the beginning you have to work to get stuff to sell and there is stuff you can buy and use, later on in the game, you can't either sell stuff, at least not for a good price, or if you can sell it, you can't buy stuff, or if you can buy it, the stuff you get isn't useful at all, or you can loot much more and better stuff than you can ever buy. People tried to solve that in various games in many different ways, however, it almost always ends up breaking the game balance in another way or for other play stiles, character classes, etc.
On medium difficulty for me the economy breaks usually while being in The Hub if I play sloppy, if I play more carefully (pickpocketing a lot, looting everything that is possible, etc.) as soon as I reached The Hub cause I can buy everything that is buyable (taking out the Khans does the trick, which is fairly easy on medium and with the right skills). I get the guns I want and usually use throughout the game (or at least until late in the game), I have all the ammo and stims I need. The Gun Runners offer a bit but at that point caps and equipment are not the problem. In Fallout 2 economy starts tumbeling down in Vault City, getting even worse through restocking vendors and the massive amount of high value loot you get in random encounters, once you have the car, the only problem is to not get killed in random encounters when traveling between Cities to sell stuff. This also renders the barter skill entirely useless.
I have similar problems in Morrowind, economy usually breaks after a few hours, in Oblivion, Fallout 3 or the Gothic games it lasts a bit longer. And, I know, others often have the opposite problem.
Does Steam offer some goodie for certain hours?
