How much to charge for shredding

[Shemp]

My neighbor asked if I would come over and do some shredding on his property but I had no idea as to what to charge him. He has 20 acres with alot of trees and overgrown brush. It's not going to be a straight shot cut by any means. He basically just wants me to hit all of the open areas that I can and not really clear anything out. Any thoughts on a price? Thanks.