I was thinking about this. If money is a really big issue, then CCW is pretty much eliminated. There is such a cost and time comitment in my state to get a CCW that I don't think anyone looking for the absolute cheapest weapon would have much cash left after the class. You could illegally carry, but that adds another risk. If you are really poor do you want to loose your job while you sit in jail? That would just make the problem worse, so illegal carry is out for me.
Legally, I would go look for the cheapest most beat to heck 12 gauge I could find. Assuming I still know what I know about guns I could do some repairs and make almost anything shootable, so long as no major springs or parts were completely gone. Trimming down the barrel a little bit would be good. I think a LEO would definately know what was up if I had a 18.25" hand sawed barrel, but something around 20 might look less suspicious, especially if I re-soldered the front bead and used some magic marker and sandpaper to clean up the muzzle. It's my grouse gun officer. One box of 7-1/2 trap loads and I'd be all set. Practice makes perfect, but just knowing what to do is often good enough, so I wouldn't need to practice if I couldn't afford it.
If I wanted to be protected for CCW type situations, I might get some pepper spray and a lockback knife. I have a Tommahawk framelock knife that cost me $5. I can open it with the thumb stud one handed, and it isn't as threatening as a gun. Almost any blue collar type guy can get away with carrying a folding knife. The pepper spray is also inexpensive, legal to carry in most places, and provides a less severe response to a threat. Also, nobody ever really "wins" a knife fight, so the pepper spray would be a way of avoiding it.