It depends on your budget to determine your entry hardware.

Low Budget = RX-550 4 GB
$125/card | ~450 H/s | ~22 Watts
*BIOS Modded

High Budget = Vega 64
$675/card | ~2050 H/s | ~200 Watts
*BIOS Modded

These are really the only 2 options you want to go with. You could go the Vega Frontier Edition route too, but those cards are very hit or miss and not worth the trouble.

We have several rigs of both types, ROI is 10 months at current prices.

If you want a pre-built and configured solution at the speeds mentioned above let us know!