It's free! I've done it for several years now. You can choose to just be Pullorum/Typhoid certified or also do AI. I do both because a lot of states require both for shipping birds and showing now.
Pullorum/Typhoid testing is once a year, AI is every six months.
It's a little bit of a pain to catch all the birds and then the testing takes about an hour for when you're doing P/T and AI on the same day, and about a half hour for AI only day. They test up to 30 birds. Waterfowl don't get P/T tested, only AI tested.
AI testing is a swab in the throat for land fowl, and a swab in the vent for waterfowl. P/T testing requires a little blood, so they pluck the feathers in a small spot under the wing and then poke them to get a drop of blood to use.
This is all specific to NY/VT, for anyone else reading. Different states do it differently, but NY and VT do it this way.