Frankly, I looked into this a while back, and found the cost prohibitive. If a good gunsmith will do it for $50, that's a steal. The best price I found from a competent gunsmith in the Houston area was $125, but VERY few gunsmiths do it anymore, because the cost of setting up their shop doesn't justify the ROI.
If you shop the Gun Auction sites, you might find what you are looking for in a new barrel. I just purchased a brand new Browning BPS 26" gloss blued barrel with 3 chokes for $150 just after christmas.
There are a couple of 1187s I just saw NIB for $165, but they only had a modified choke. I KNOW that I've seen them for a lot less than that recently.
The math for me added this way: A thread job and 3 new chokes at super best price I could hope to find for about $140, or a brand new barrel with 3 chokes for about $175.
Buy a new barrel and sell your old one. FWIW.