-Size: 10x10x7
-Nether compatible
-Speed: 10 minutes/ stack of soul urns
-Price: it uses 3 BDs, 1 block detector, 1 turntable, 2 sticky pistons, 6 hoppers, and various redstone elements
General pics (explained below)
Looking at the second picture you can see the basic concept: A BD to place urns, a BD to dispense ground netherack into the hopper, and a detector block to see if an urn is present.
At the heart of the device is a BD counter powered by a turntable with two torches for maximum speed. Images below
The contents of the BD
Advantages:
It is compact, 100% efficient, cheap, and nether compatible. It can also be stopped and restarted at any time and can run out of materials and resume when they are available without any loss.
Disadvantages:
I'm not sure about how fast do you consider it. It definitively can't keep up with advanced urn making machines.
I hope you consider this helpful and if the explanation wasn't clear, here is the world download, it also contains the simplified version of the circuit.
http://dl.dropbox.com/u/75977115/Test.zip
Thank you FlowerChild for making this awesome mod and for saying that we need 32 blocks of steel :)