You might get more interest if there was a cover charge

I think you should charge 20 bucks, and require an AMA membership. People like to be charged for stuff so they feel they are doing something important. Donate the proceeds to Queen Elizabeth's Foundation Promoting Equality for Disabled People. They help people with brain injuries from accidents.
http://www.charitychoice.co.uk/charitydetails.asp?ref=8830The Queen loves a nice tea.
Interesting side note, a medical group recently did a study and found that people recovered faster from the flu if you gave them an expensive placebo than if you gave them a cheaper generic equivalent placebo.

It's all in the mind.
Better yet, tell them it costs 20 bucks, them let everyone in for free when they show up. That'll make them feel VIP.
Scot