I'm not sure what the cost is - I remember someone telling me that here in Maine they'll do it for free. I'd just check with them I guess - it might be something where it's in their best interest to have an understanding of what's going on with local chicken flocks, and also for outreach purposes when similar questions come up. Then again, if it's not something immediately obvious I assume there would be some lab work involved which someone's going to have to pay for. Maybe they have it in their budget already.