As a small corporate user
and in the firm beleif that this smacks of a consultancy firm trying to get outsourced work at exorbitant rates, the cost of investigation should only be borne by the people being investigated if they are subsequently found guilty of something significant, as a sort of "costs" order associated with any fine.
I pay for the Information Comissioner already via my registration fees. If these are not sufficient, then they should be open about this and raise them.
The alternative is that loads of "anonymous" or malicious complaints will suddenly come in and companies will be subjected to intrusive scrutiny and then handed a bill, even if nothing untoward is found. I can imagine the time and trouble an investigation would put my company to and the costs that would be levied by "experts" acting on the ICO's behalf.
I get very nervous of institutions where the investigator is also the judge, and giving them a financial motive to conduct investigations (keeping busy => empire building) could lead to a perception that they are serving their own interests, not that of the public.
Whilst I do wish to see the office made more effective, this particular avenue is not one to go down and would taint most peoples view of the ICO, which should be prevented if possible.