Of course, if you're feeling lucky, you could try to replace the disk inside with another Seagate drive (they don't sell the model ST318203FC in their on-line store). The closest I can find on the site is a model ST318452FC. At $340, it may be worth the chance if it works, compared to $1,100 to get a disk from NetApp.
I've done this and it works reasonably well, in fact I ended up buying a DPT branded SCSI eurologic disk shelf and filled it with IBM drives, once the drive firmware had been overwritten with NA00 or whichever version it was it all worked fine. The filer wasn't happy though with daisy-chaining the drives and I was using an OEM qlogic scsi card. This was on an old "spare" F540 that I had lying around, once it had the disk upgrade it served quite happily as the main fileserver in an office of 50 or so users.
Chris