Assuming you wouldn't get caught, what is the least payment you would want to plant an eavesdropping device at work, just once.

Depends who is asking and why. Spying on someone's spouse, boss spying on coworker, business competition -- not under any circumstances. Feds or cops as part of a legit investigation (with warrant) ...hmmm, why would they ask me? But I'd do it for free if I did it at all.

You pose an interesting question. With advances in technology an dramatic price reductions, sophisticated devices that costs thousands of dollars ten years ago, are available for under one hundred dollars today. As a result jealous suitors and unstale neighbors now have the same capabilities as those who were previously thought of as "upper tier" threats. Unfortunately the vast majority of folks offering "bug sweeps" do not have the technology to find these new threats. An uneducated consumer would undoubdetdly find it difficult to select a qualified service provider.