They should still sell for a year+ As for price drops, probably never, as they have no real reason to as of yet, and once discontinued they tend to increase in price.
They normally go on sale when the next series of cards is announced to try and get rid of stock. I'd wait until the 800 series is announced to get a second card.
Hope this helps
no one really knows when the price will drop. hardware priced fluctuate on a almost daily basis. you dont really need to worry about it not being sold. even if they stop making it you can always get one of ebay or something