I am pretty sure that even if you called a local exterminator, he will not quote a price until they come to inspect the building. But, they will come and give a free estimate. I would call a few and ask each what kind of service they provide.
Personally I have not had to deal with that issue but if it were to come up, it would be my top priority. Once it was dealt with, I would consider regular service. I have no idea what that would cost but I would guess $50-$100 per month.