RX sires cards do not look too bad for progpow
https://progpow.pro/. Looks like a 580 can get 80% of the performance of a 1070 for less then 1/2 the price.
RX 570 = 11.23
1070 = 13.3
That's at default clock with default power draw. The card will draw roughly 200-230W while mining, so it is pointless. Undervolting it down to 1150-1200 core should achieve nearly half the power draw.
I think the power you use to do mining is very high, imagine if you have a lot of cards then the power you need is very large and not profitable.