Sounds close
I would never say a smith is charging you too much, but it should be charged by labor and parts. If the spring needs to be replaced, it should be close to $12 retail to you. Labor should be close to an hour. He should have a sign up giving prices for labor and he may charge a standard fee for trigger jobs. Don't be afraid to question him about it. If he is a straight up guy, he will gladly tell you about his prices and how much time it should take him to do the job. Of course he will have to estimate the time since no one knows exactly how much time it will take until he starts the work. If the spring needs to be replaced, the time will increase due to the work having to be done twice. You have to try to get the weight right before you know if the spring needs to be replaced. Just ask him to expalin the charges to you. He should break it down on the estimate as well as the final bill. $50/hr is not unreasonable for a man that has spent the time learning the trade.