The price I saw for it was $200 on newegg. For the 1070ti price I saw was $450 and would be mining neoscrypt or equihash. My calculations could be a bit off but so far it seems the 580 would ROI faster?
RX 580 cards start from $250 on newegg, and that's for the most basic 4gb versions. Decent cards with decent coolers are closer to $300, and the 8gb versions are more than $300. Current high profits from these Polaris cards are all from ETN, which is a new coin that might go down really fast. After that it's back to ETH, and you're not likely to get 30 MH/s (as whattomine suggests when you select rx 580) from the cheapest 4gb rx 580 cards cause these days they often ship with weak hynix and elpida memory chips that you're lucky to get 27-28 MH/s from. So it's less than $1.5 a day per card.