Xsan per Node

Each machine that is connected to the fiber, yes. That includes the metadata controllers (I always recommend 2 per SAN -- a primary and a backup controller), as well as each workstation.

Xsan, while not "cheap," is very inexpensive compared to competing products in its class (SGI, Sun, and ADIC offer alternatives at $3500 to $10,000 per node).

For a "typical" Xsan deployment that can do HD, you're looking at $26K for 2 RAIDs, $5500 for a Qlogic 5200, $10K for a pair of Xserve cluster nodes with FC cards and 2 GB of RAM as the primary and secondary MDCs, and maybe $9K per edit bay ($499 for a FC HBA, $300 for a pair of 25 meter fiber cables, $400 for optical transceivers so you can make the run to the edit rooms, $999 Xsan license, $4K for a top-line G5 with a 7800 Ultra, and $2500 for a pair of 23" monitors).

Compare the $60K for the above listed equipment that gives you ~11 TB of shared storage that can do HD to 3 stations, with the price of 3 Avid workstations and 10 TB of Unity, and see a number WELL into 6 figures.

If you look around a little bit on the web, you can find new Xsan licences for around $400 on ebay. a set of 10 optical transceivers you can get for around $250 on ebay. Qlogic Sanbox 2-16 Fibre channel switch (16 ports) start around $1000 on ebay, but they don't come arond often, so you need to have some time.
so, if you have some time, you can cut costs substantiallly for your SAN. As advised before, you should plan for 2 SAN controllers.
Best prices for Xserve Raids I found so far at
http://shop.store.yahoo.com/macresource/xsandraar.html.

I have to imagine the $400 Xsan licenses are academic licenses, and thus would not be legal to use for a production studio, unless it was somehow related directly to educational use.

The 3 I bought for around that price were NOT academic licenses.