Whats a fair price

I have 81 acres in Jefferson county. Father sold gas and oil rights to Great Lakes Energy in 2007 for a very low price. He passed away 4 yrs. ago and recently we have been getting offers to buy our rights. Don't know if this means they are going to drill soon in Jefferson county or not. I would like to know a little about the price I should be looking for before we negotiate. Thank You for your help.