If you don't mind using a couple of sub 1TB drives keep an eye out for old laptops, set top boxes and DVD recorders people throw out. Many of the last two examples don't have easy access to the HDD (you have to pull the entire unit apart, and some use security screws), even some laptops don't have an access panel to swap out the HDD.
I've got a pile of sata drives here that cost nothing, laptop and desktop types. You'd be surprised how easy it is to come across 500GB size, and quite a few of them are WD or Seagate.
