i can't help you with the price (like peanut my quigley was spayed before he left the shelter), but i can tell you that neutering isn't necessarily going to make the humping go away.
not that you shouldn't neuter him - it's a good idea, but there are other reasons for dogs to hump, such as stress/excitement and display of dominant behavior. my dog was an early neuter (3 months, way before sexual maturity), and he sometimes starts humping when he gets really excited. he also learned to lift his leg after he was over a year old.
your best bet to eliminate the behavior is firm, consistent training.