If you are looking for something for a budget, guns are pretty hard to practice with without spending money... Unless dryfiring counts, which it does... kinda. I know that it isn't what you asked, but have you considered pepper spray or a knife, or something like that? You can get a decent size serving of pepper spray for not very many dollars, and a good knife for (again) not much.
If I were in this position, I would probably go for the knife/pepper spray approach, until I saved enough to get a used or even an abused older revolver, or even a new Armscor. Another option, if you are comfortable with it, you might be able to find a good deal on Gunbroker on an older (not really old, like from the 1800s) shotgun. There are plenty of them out there to choose from, and if you have a hacksaw you can chop off some of the barrel if you like.
Take a look at this one. I don't know about it, you would need to do your research, but...
http://www.gunbroker.com/item/592507233
Older bolt action shotgun. Not pretty, and you won't win many skeet matches with it, but it will probably work!
These kind of guns are out there, looking for a nice home! Your local shop might have something like this too. I know it might not be what you are looking for... but I figured it might be something you hadn't thought of.