Greeting from the snow day capital of the world!

I just sent out paperwork for my 2nd suppressor. I quick visual audit of my harem of rifles was very disturbing, I have only 1, yes 1 rifle with threaded barrel.
I want to thread the barrels for the suppressor quick attach mount thingy (technical term).

1. What does it cost to get a barrel threaded?
2. what is the minimum OD that I need to be able to thread a barrel