Actually setting up this site could technically cost the person nothing if they had the equipment already. All you really need is a good firewall, the know how to set it up, a public ip address with a high bandwidth line....... actually the more that I think about it hosting you own webiste is actually more expensive then it usually is to rent web space. I know my GF rents webspace and I don't think it is costing her more then $100 - $150 per year for the space. She also has a pretty similar setup, same type of message board and what not. As long as you don't get charged for the bandwidth usage hosting costs for this type of message board are quite minimal.
But all that being being said, I don't think it would be a big deal to throw $20 to the site to help it out.