What you'll need to do is find a large piece of land in a remote area for cheap.
If you use Craigslist search in the areas where you would like to bug out to...for example Mohave County AZ (Kingman, Williams). You can find 10 acre plots for under $20,000. I usually use a keyword of "Off Grid" or remote for my search.
You want to find a piece of property far away from neighbors but close enough to town so you can get water and supplies if you don't plan on putting in a well.
After a certain period of time, you may have to actively begin to build on the property to meet county requirements which means you would have to file and pay for permits.