670, 680, 760ti, 770, 780 would be enough. Cost of 690 won't be decreased much, I guess it would still be at least $900 when the next 700 gen comes out, and slowly decline to $800. I predict this based on the history price of 590
Battlefield 4 will not be a major jump in graphics like 3 was. It is using the same engine with a few improvements and of course optimizations. I'd say anything in the 570GTX range will run it on ultra.