Once you have the systems and app setup it's more like "let it whirl"

I paid about $650 for 3 GPUs and another $300 for other system parts, the system already paid for itself 4 years ago I am basically re-purposing it. So my only hardware costs this time around is about $1300 for 6 GPUs plus electricity costs. At this current ETC price, I should get my return on investment by next month. So ROI is roughly 4 - 7 months for me. ROI will vary on electricity costs, rig costs, and price of coin you are mining. I hope this helps.