I would have to agree with several of the various different statements.
#1 - If its a real investigation, and you're charging for admission from non-members of the investigation then it sounds more like paranormal tourism, and I'm no big fan of that. Kind of like all the ghost tours popping up everywhere. However, I do understand the need by some historical societies to charge for access to a location in the interest of upkeep and covering the cost of maintaining the location and insurance fees.
#2 - If its a charge or fee requested by a group to cover expenses for shared equipment and travel fees, then I really have no problem with that. There are a considerable number of costs involved in having a paranormal investigation group, and no one person really should have to cover those costs alone.
#3 - I'm not really a big fan of mass organized investigations. To have a real investigation you really have to be familiar and comfortable with the individuals you are going with. After all your trusting that they will not do anything to put you in danger. And you have to be able to trust to individuals with you to make sure that nobody is introducing possible noise into the collected evidence. Same reason a group which is too large is also not conducive to a good investigation.
Ultimately I think we would all love to be able to make this from a mere hobby or passion into a full time profession. And in doing so there must always be some way to bring income in by doing it. I don't think that necessarily is a bad thing, but rather just a fact of life. But I think its important through-out the process to always remember to provide to those who need your help, without charge.