The new Blendergrid render farm uses Amazon EC2 for rendering. By entering the preferred rendering time, you can influence the job price.
Richard van der Oost writes:
The Amazon Elastic Compute Cloud (EC2) is a great service for resizable compute capacity. I found out about EC2 about a year ago, and immediately thought it was a great opportunity to build a virtual renderfarm. It turned out to be quite a technical challenge, but with the help of some awesome web developers and coders, blendergrid.com was live. I have been using the farm for my own projects for a couple of months now, and it’s time to make it publicly available because I think a lot of people can benefit from it.
I have tried to make the web-interface as simple as possible, so anyone who uses Blender is welcome to use blendergrid. I’m planning to keep improving it and implement requests when I receive feedback from users. The great thing is, the prices for Amazon computers are not static. This means that if you start a render job when the demand is low, you can save a lot of money!
For more info, check out the website at blendergrid.com.