Not anytime soon. 500GB drives are over $200 right now, and 750GB Drives are $400. As far as I know, no internal 3.5" 1TB drives exist, much less external. Expect 1TB drives (internal) sometime around the beginning of next year, or maybe the end of this one. But they'll still be close to the $350-$400 mark, if not higher. 1TB drives in the $200 range? I'd guess 1.5-2 years from now, barring any unseen technological advances.
EDIT: My bad, Seagate's 500GB is $230 normally, but $150 because of Newegg's Holiday Sale.