Hello there Andrew!
As you probably noticed, our render farm is also listed in the link you've provided - RenderBuzz.
I can walk you through our process of using our service, and I'm pretty sure it will be similar in other
farms mentioned.
To start using RenderBuzz services you should register and activate user account.
Use our calculator to estimate the render cost of your project, as Scott mentioned before, I also advise you to buy a little more rendering points than the calculations and make some test render before submitting main job.
To estimate time and cost, you have to provide the number of frames to render, average render time of one frame and your CPU model.
Then you can prepare and upload your project. In our service you can do this via dedicated plugin or manually (all needed manuals and plugin are placed in *downloads* section at our page).
Next step would be submiting your project to rendering queue.
In our service, you will receive an email after completion of rendering. Your rendered frames will be available for you to download from Dropbox or directly from our website.
For every new user there are some free rendering points given for testing purposes - that's the best way to see for yourself how the process is going.
If you'll have any questions, feel free to contact me, I'll be glad to provide you more informations in this subject.
