And it was once again Rackspace who stepped up to the plate; they have kindly donated us more cloud servers. I also use Rackspace for one of my personal servers, and when I went back to their admin console this time, I noticed that they've added a lot more services to their offering.
I am setting up these boxes as I write this. A huge thank you for Rackspace for their support of this project. And if you are interested in using Rackspace cloud servers as elastic build slaves, jclouds plugin is your friend.