There's a lot of cheap land in my state of Texas right now. My husband and I are currently looking for some property and it's definitely a buyer's market, I constantly get notices of properties I'm watching dropping in price. Of course, Texas is in a horrible drought right now, making homesteading more complicated. I'm hoping that with careful permaculture water harvesting and storage practices that we'll be able to overcome that problem, but we're also looking for something on or near a lake, just to be sure we have access to water. As you can imagine, those kinds of properties are more expensive.
For the absolute cheapest, you can look in the beautiful mountainous area near big bend. I've seen 10 acre properties for 3k. Of course, that is in an area where you are in the middle of nowhere (nearest town an hour's drive), don't have access to electricity and have to dig a (deep) well for water. I'm considering buying one of those properties just for shits and giggles. It is a really beautiful area. A good place to start is: http://www.landsoftexas.com/texas/
But as others have said, you get the best leads just driving around and looking at for sale sites and then going to the websites of those small local realtors.