For a group or employees of a corporation to be bonded is very expensive. Coupled with equipment costs, and the eventual training and/or certification process that an insurance company may make you do (if they will even cover you), then I think groups would need to charge. Unless you have a lot of clientèle, then how do you expect to pay for it? Charge lots and lots of money that's how. Who can afford that? Are you going to work with some realtor and take a cut from commission, take rich enthueists on "ghost hunts", or what?

Yes a bond can be expensive (ex: a 2 year $50K private investigator agency bond for New Hampshire is about $400), but what could it cost you if a homeowner claims you destroyed their $10K antique Persian rug?

Yes but how much is it for a paranormal investigator? I don't even know if most will bond you. All I'm saying is that if people require a field full of "part-timers" that are generally your average person are expecting incorporation and bonding and even permits, then expect the field to die or become very expensive.