I have tons of mini nukes. The only problem is that the only weapon that shoots mini nukes is the Fat Man. I've seen it a few places and and never had the caps to buy it. Is there a place in Fallout New Vegas where I can get it for a low price or free?
Well, merchants don't charge different prices, so the only way to lower the price of an item is to increase your Barter skill.
You can find Fat Men in the following locations (source):
Be aware that most of these locations are dangerous for a low level character.