Other than obvious increase in price what are the functional difficulties in using and mass producing silver bullets to kill were wolves?
You may be interested in this. The author went to the trouble of making and eventually shooting some silver bullets through ballistic gel and talks about the difficulties of making molds etc. There were interesting results due to the hardness of the silver. It also has a page on making silver tipped bullets, by filling hollow points with silver which is apparently easier.
Can you silver plate the lead and still have it work?
You can make the magic how you want it. Assuming lead is cheaper (and slightly heavier) than silver, maybe you could make lead bullets and then silver plate them. If a thin layer of silver = silver bullet for werewolf purposes that would save a lot of money.
I am thinking now of old fashioned firearms where the bullet was just a piece of metal and the powder was separate. If these are modern bullets where the propellant is integral to the bullet you would not want to silver plate one of those.