The bible says don't muzzle an ox, and give honor where honor is due. In other words, it's ok to receive something back for service rendered, even in the name of God. By the way Balaam's sin was not receiving something for a job well done but for receiving something in order to do evil. Your asking whether a prophet who gets paid is of God but look around you nearly every church pastor, even your church pastor, is getting a salary or something for what he does.