At 300 MH/s mining ethereum my rig is making around 0.526 eth a month
( with current prices that's about $1013 a monthly)
Main Rig Components
Motherboard gigabyteH110-D3A
Cpu I3 7th
Sata 250gb
Ram 1x 8gb
2x corsair rm850 gold plus 1700w
5x rtx3070
Total cost $7500
I will get a few more gpus for eth just because it is still profitable for the moment, but I will get Bitcoin miners soon because of eth pos ..etc