Your prices look pretty good for those size sacks. If you buy from someone who sells firewood and buy in larger quantities you can get your per piece price lower. It all depends on how much wood you go through in a season. Sometimes the convenience of just grabbing a bag of wood at the store is worth the $15. If you are cooking on just wood that might not be so practical.
18.5 WSM, Green Weber Genesis320, Cast iron firepit(w/grill), and a Copper Weber 22" OTS