Well, for a TB+ NAS, your going to spend around 700 bucks. Before you could buy them, I was using freeNAS and Linux zero raid to build my own boxes. For the money ( assuming you have gigabit networks) I just think these new NAS systems are pretty good. They are quiet, cool, and safe with raid 5 options. You could also get an empty setup from Buffalotech or any Intel, and add large drives in a spanning schema as you progress. You'll save money over time by adding extra (up to 5 for most home NAS solutions) as they drop in price.
Check out Tom's August 1st issue on building you own.
It fun to do, if you can do the up keep.