Don’t believe the scare tactics about DE, the worst that could happen with it is maybe it wont work as well or as fast as you would have hoped. But at least you are not out $2000 to $4000 bucks, and your house is not sprayed with toxic chemicals. Try it as a first step, its cheap and safe and you have a 75-90% chance that it will work.
Be careful of fear mongering about DE from those that may have an agenda. It is EDIBLE for humans, so you may as well try it. Its like getting advice from a Honda salesman why you shouldn’t buy a Toyota — he is an “expert” on cars, but only on Hondas.
Bottom line is it worked for us and there was no down side to doing the DE, as a first step along with the other things I mentioned above. If it doesn’t work, then you can go about spending $80 with Lawrence’s advice above. But avoid chemicals, they don’t work and they are toxic, especially if you have kids.