There's a couple of ways to do it. One might be to see what other lots are selling for in the area. Sometimes this is easy, sometimes not, just kind of depends on where the lot is and the characteristics of the lot. If it is the only lot left in a neighborhood, you could back into the price from the values of the homes and construction costs. Another way is to check with custom builders who might have customers looking for lots and have them set a price. Your realtor shoud be able to assist you setting the price.