I have all my silverplating done by Anderson Silverplating right next to the Bach factory in Elkhart. They are a great company and do the best silver and gold plating. The fastest i can priority mail to them and get back from them is one week, but usually it takes about two weeks. (rarely longer)
I include the plating in my price, but sometimes players want a mouthpiece replated. For that i have been saying $25 for silver and $70 up to $90 for gold. That gold price can change with the price of gold. There is prep required.
I do all of the prep for plating on the same day right before shipping to elkhart. I might make a mouthpiece on monday and not ship until friday to ship with other parts.