Another factor for you to consider is that properties that are cheap are usually not listed in MLS.
The owner figures that his $200 commission money would be better spent on other things than on getting it advertised and leased. So, when you're looking for low-priced rentals, you should expect only a small fraction of them to be listed in MLS. The majority will be the owner's sign on the lot.
If a property is listed in MLS for a poor area, it usually has been upgraded including alarm system and security, and the price reflects improvements.
Bear in mind that owners always put the highest price they think they can get for something, not the lowest. If you bargain with someone you don't start with your lowest price to sell to them -- you'll only go lower. This means some properties in MLS are overpriced and negotiation is expected.