Do you currently have a reference 290, or is it an aftermarket model?
What's your reason for wanting the upgrade? If it's just more FPS, going to a 980 likely isn't going to give you a worthwhile increase, especially if you have an aftermarket cooler and can overclock it.
If it's that you want to get rid of a loud reference blower and get a little more performance, or just really hate CCC, the B-stock 980 might be an option. Going rate on a 290 seems to be around $175, so it will cost you ~180-220 (depending on shipping, taxes and whatnot) to get a 20% performance increase. Unless you really hate running that 290 you'd be better off just buying another 290 and running them in xfire until Pascal arrives.
Going with a 980 Ti would set you back 425-475 out of pocket, but you'd probably see a 60-80% performance increase or so depending on overclocking, which would be much more noticeable.