assuming you have a suitably large target to back up to, rsync (possibly broken up into chunks or managed by a set of scripts) may be suitable. (for the pedants in the crowd: it can still be used to make a backup, depending on how you structure the target, whether you use --delete or date stamping, etc.)
it's not clear from your question whether you're interested in backing up the current contents of your NetVault elsewhere, or if you're looking for a long-term replacement for the NetVault (sounds like maybe both?).
I have had good success in the past using ZFS on a suitably large disk array (a Sun Thumper at the time) running Solaris 10 as a feature-compatible NetApp replacement (at about 1/10 the cost). Depending on your feature requirements, this is worth looking into - zfs is pretty sweet (as are many of the other new technologies Sun introduced in Sol10).