It depends on the lay of the land, home site locations, ease of hooking into utilities, does one have a well already, pre-cut roads/driveways, etc.
These are all factors that contribute to the prices; but the most important to remember is that these are just what they are asking for the properties.
An owner next door could ask $13,000 and acre if he/she chooses; but that does not mean that it is worth 13k/acre.
The same goes for homes; we very often see someone try to sell their home for what they paid for it 6 years ago, but the neighbor next door will sell their home for what it is actually worth, and it will sell quickly while the overpriced home sits.
Hope this helps.