More than the seller wants and less than the agents want. Sorry for my silliness, but this is often the case. Commissions are not set and can be negotiated by the seller. Often land is higher than residential because the amounts are less.
My recommendation is to meet with some local agents who specialize in land sales. They will tell you how much they charge and you can decide based on their presentations who my represent the best value for you. This is a perfectly reasonable question for you to ask, but not as easy to answer. Consider this with your interviews, some agents focus on commission (high and low), others on getting listings to pad their inventory and may recommend higher pricing than others. A good agent will tell you the truth about the value, charge what they need to do a good job and listen to your circumstances. Best of luck.