monetary compensation for acoustical design services?

how are your fees for acoustical design being determined? cost/floor area? cost/volume? cost/construction cost? I would love to hear some numbers? Please, feel free to PM me if don't want to advertise rates that may be subject to change.

I have interviewed many. I got rates from 10k to 20k, depending on the designer's distance from my place. The rates included airfare and perdium, so that they could provide some on-site analysis, management and room tweaking. Many people think that studio designer's are a waste of money. I don't. I looked for someone with the ability to provide Architectural and Engineering documents, drawings, etc, one who had a proven track record with rooms to visit, could provide Errors and Omissions Insurance, so that if they design a room that has a structural/mechanical flaw, I am covered. I wanted one with CAD abilities so that they could send files to the local contractors for bidding, etc. I finally decided on Francis Manzella, because he was the only major with rooms in my state for me to go to, and they were killer. He could not stamp drawings for the local building commission, but my dad can, so that was no biggie. If you are giving something away for free, people are going to know that you are not in demand, you have nothing of worth to offer, and you have no clientele. There are many things to consider. Unless you are familiar with local building codes, permit procedures, city business zoning laws/codes, etc, it can get hairy.I would charge, but I would first get an attorney to get a contract together, so that this guy doesn't build a room, have a fire, structural failure, etc, and come after you for damages.