I think for your price range, there won't be any upcoming AMD cards that will be worth it. The 390 and 390X are supposed to be the only new GPUs in the next generation and they will cost significantly more than your price range.
With a new GTX 970, you'll also get a free copy of the Witcher 3 to help with the value proposition. The Witcher 3 is a fully next-gen PhysX game, which brings us to the other issue with waiting for the new AMD cards ... you still need to decide if you want to be in the Nvidia ecosystem or not. This is a very key decision point that most people pass over. The fact is that there are two different user experiences that begin after the purchase is made that depend upon which ecosystem you have joined.
In general, you're going to get more graphics settings and image quality options with Nvidia, like PhysX for example, and Adaptive VSync. You're also going to get consistently better driver support, better game compatibility, and lately lower power consumption, heat, and noise. For the most part, AMD is lacking in comparison.
If history holds true, the reality of the 390x will underwhelm its hype. If history also holds true, Nvidia will release its response, likely in the form of a GTX 980 Ti to rain on the 390x party. This card will be either faster, a better value, or both. Flag this post and come back in June-July to see how well those statements hold true.