Old thread but a great thing to consider.
We buy and sell land all over the country and can tell you it varies quite a bit. Location of course matters, but the also the development on the land. Drainage, fertility, timber, water access, road access, proximity to "civilization", land taxes, etc etc etc.
The best thing you can do is check out market values are to use zillow and landwatch. Make sure to use appropriate filters to see what land is listed for with the characteristics you want (size, location, etc). You should be able to see comps.
When you're looking to buy then make sure you buy from a discount land seller. These are sellers that buy properties that people don't really want and then sell them at a discount. There are so many properties available around the country offered at a huge discount which would make the entrance to homesteading and permaculture much more inviting.
There are many out there.