Depends on the location... In my area, there are a lot of homes on the market for between 15 and 50k. Taking out a 30 year mortgage keeps the mortgage payment pretty low. It's not hard to at least break even. If you can break even for 30 years, you're in great shape! Because after that mortgage is paid for, you just have maintenance and taxes. The rest is profit, including the sale of one of those homes (which hopefully would appreciate.) Don't forget, if you have a fixed interest rate, your monthly payments are going to be steady. And, generally speaking, home prices increase as well as average rent. Thus, even if you're losing $50 a month now, 10 years from now, you may be making 100 a month.
edit: I have a property with a $300/mo mortgage. Rent is $500. After taxes, I lose about $250 a year. But, there are all sorts of things that happen with income tax:
I can write off mileage for going to the house. I can write off any improvements or repairs I have to make. I can write off tools I need to purchase to make those repairs. I can write off the taxes paid on the house. I can depreciate the house if I wanted to... So, while up front, it looks like a $250 loss over the course of the year, I gain more than $250 in equity in the house from my mortgage payments as well as the increase in property value. Of course, within a few years, I'm going to have to replace the furnace. That'll be about a $700 hit. Other than that, I can't think of any other expensive repairs... roofs are relatively new.