Who is charging you a$100 for a cell change? I would like some of that work ;-) You can purchase cells at most any store that sells them. The trouble will be the gaskets. Here you need to know the size and then order online from a supplier. Then have the proper grease to lubricate it. Of course use finger cots and plastic tweezers. What I am getting at is if you are trying to get into elementary watchmaking go for it. If you are trying to save money I am sure you can find a qualified watchmaker in your area to change a cell for a reasonable cost. Check out American Watchmakers - Clockmakers Institute and Welcome to NAWCC for watchmaker referrals in your area.