You can make out the outlines of Iowa which has higher rural land value than neighboring states. Some of the oddities on the private land map are due to the history of how private railroad construction was subsidized by the US government. The government gave a corridor of land to railroad companies that they could sell to make money to pay for construction along certain routes:
Today, you can still see strips of private ownership along these routes such as the strip through Nevada where the Central Pacific railroad runs and through Arizona that is a legacy of the Atlantic & Pacific route.
The main thing that makes land valuable is having more neighbors because higher population density means more customers, more jobs, and higher productivity per acre as shown in this map:
And here is a map of all the census blocks where nobody lives:
If we switched our tax system more towards a land-value tax, it would increase population density in cities and also make land cheaper.
The wealthy landowners who own the most acreage tend to buy in areas with cheap land. Almost half of the privately-owned land in northern Maine is owned by just a few families!
Looking for more data about real estate prices? Numbeo has some interesting numbers although they seem to be crowdsourced which can be inaccurate. According to them, the USA has some of the most affordable cities in the world when adjusted for earning power. Of course, for travelers, other things are more important than real estate for determining cost of living.