Yes, the Sun Fire Xs are costly...
Here, 35k euros for 48 x 1TB by example, or 22k for 48 x 500GB...
Our 12TB HP is around 6k. So 12k for almost the same as the 22k
But if you use 1TB disks on the Sun, you end up using half the Us (and save some power) in your bay; which might be nice if you are tight on physical space...
It all depends on your needs.
Note that I think the Sun Fire X uses software RAID (from zfs)...
JD