I do price checks all the time and with the new nVidia cards, the RX 580 8GB cards are now down to $180 on NewEgg. I believe AMD probably use the Polaris cards to flesh out the low price points for a while anyway.
The new RX 5700 launches at $379 which is more of an enthusiast card.
Eventually AMD will have some lower price point cards to fill out the lineup with the TSMC line carrying the load.
nVidia is using Samsung to make their new cards which leaves AMD and some mobile phone vendors at TSMC. Samsung has wanted to become more active in the contract manufacturer sector.