I have a contact who is able to get 1tb WD enterprise RE3 drives used from server farms when they upgrade to 3tb drives. He sells them for cheap enough that it's hard to pass up. If I wanted to run 4 ...

I generally avoid Seagate due to anecdotal experiences (never had a single WD drive fail on me), but this article gives an extra reason to avoid the 3TB variants. At least the 4TB ones are pretty okay ...