What's the best way to recruit participants for doing remote evaluations of my website?

I'm already using a service called Usertesting.com and TryMyUI.com and I've exhausted most of their participants. I would recruit directly out of our pool of subscribers, but I need people who haven't already used our service. Also I'd like to match a general demographic of college-level educated and aged 45+. I'm planning to pay $25-$35 per participant for a 1/2 hour evaluation. Any help would be greatly appreciated.