In the place where I live, electricity is less then $0.08 and I can get 10 second-hand (6-12 months used) moded RX470 4GB (29Mh/s per GPU) for the price of one R7, so it is 300 Mh/s against 90 Mh/s for the same money.
But what about the electricity? But for some reasons rx470 has a limitation to mine crypto with large size of DAG file, right? But I prefer to get some rx480 rather than Rx470 4 GB.
My country it costs 0.1 for KWh
It may become a surprise for you, but rx470 can mine not only ETH.
Nowadays the best ROI you can get if you can buy cheap second hand GPUs. Of course 8GB better than 4GB but you need to look at quality of each GPU, the price and may be any other factors before make a decision.