Wow! $4,000 does sound like a lot to me but I'm sure a lot has to do with the size of the treatment area, too. If I were you, I would get at least 2 more estimates. Perhaps your realtor (if you trust them) can give you names of people who do good work for a fair and reasonable price.
Good luck and keep us posted!

Hello,

I live in the paradise of ants, Amazonia. My yard had a lot of different infestations from leaf cutters to little fire ants of multiple species. I purchased a product here called Natucid and it works great. You spray the ants, they take whatever the active ingredient into the nest and in a few days, no more ants. The site is www.natucid.com.br, they have an English portion. I don't know if they export or the like, but it is the cheapest, most natural stuff I have seen.

dk