Powered or Non-powered?
I recently bought four 1TB External Hard Drives; powered. Cost is between 3.4k - 3.7k. If you want portable, non-powered, cost will go up to around 4.5-4.7k.
As far as brands go, there aren't many choices. Seagate and WD are there. Both are good but I usually have better luck with Seagate but Seagates also cost a few hundred bucks more than WD.