It will depend on whether you go with Max or with Maya, or mental ray.
With Max and BackBurner, you can set up a render farm of 12+ nodes using your one Max license.
If you use a different render manager, then you'll need 1 Max license per render node.
With Maya, you get 5 Batch licenses with each seat of Maya, so you would need multiple seats of Maya to have 12 render nodes.
Doesn't matter what render manager you use.
If you go with mental ray Standalone, then you'll need a license of mental ray standalone for each render node.
You cannot purchase the Network version online. The online stores sells Standalone only.
Edited by: stephenblair7080 on May 14, 2010 5:16 PM
// Stephen Blair
// Arnold Renderer Support