How can I kill black ants?
boric acid (aka orthoboric acid, borax) works VERY well for under $5. Look for a tall white squeezable bottle at Home Repot or the like. Then lookup a recipe online with grease or sugar/jam for proper mixing ratios. Taking the bait back to the nest to destroy the babies is exactly what the boric acid does when used correctly. I wouldn't be surprised if that's what the exterminators are using, with a $345 markup for their "expertise". 

Even though it's powerful against bugs, it's basically harmless to pets and humans, having the same LD50 as table salt. That it's cheap, safe, and effective, is why it's my favorite ant+roach solution.