What is an inexpensive but effective way to see if my wife’s ex has us under electronic surveillance?

I think my wife's ex may have in some way "bugged" our house. He has often said things to my wife that only she and I have spoken about in the privacy of our own home. We already discovered a keylogging program he installed on her old computer and friends of his has warned us that he might have placed some sort of eavesdropping devise in the previous house that we now occupy. Our funds are limited so we are limited to as much "do-it-yourself" as possible. Any advise?