That depends in part on the age of the home. The more modern ones are really very, very nice. They're also built to higher standards. Older ones tend not to be as nice.
You're dealing with two different issues here. One is the value of the home itself. The other is the value of the land. How much does 1 acre of land sell for in the area? To that, you'd add the value of the home--which could be anywhere from $15,000 to $75,000 depending on age and condition.
Keep in mind, too, that it's not just price, but the terms that can make a deal desirable. What sort of financing, if any, is the owner offering you? Again, it varies geographically, but if the deal was something like 10% down with the remainder payable over 20 years at 6%, that'd be pretty good. But if you have to go out and find your own financing, or if the owner is asking for all cash, or offering a deal like 20% down, 12% interest, that would be far less desirable.
So: Break down the value of the home and the land. Then consider whether the financing (if any) is attractive.
Hope that helps.