A quick crunch of the numbers shows that 10K people contributing just $3.00/month would yield $360,000 annually. $3.00 per month is less than one copy of the Sunday NY Times (ok--cheesy example).
I am amazed that people refuse to contribute unless it is mandatory. Maybe one day I'll reach a point where nothing amazes me anymore. If it must be mandatory, then so be it. I would recommend $5.00/month for kicks and giggles. Of course, there will be some who will continue to volunteer more.
Heck, I was spending $30 a month for the Chicago Trib, daily and Sunday. Decided to drop it and send the money here. With my next donation, it will just about equal the amount of money I was spending on the fishwrap. (I couldn't even use the Trib for the cat litter box, only the Wall Street Journal works for that one...)