At the height of the last crypto boom, with elevated GPU prices, you could expect to make back your investment (with electric costs) in about 200 days. Assuming that means a 2.5% per-day return, that could be extrapolated to be ~60% return for the rest of the year, which figures out to about 27% return for the entire year. That's back of the napkin as it assumes you only run the machine for a year (warranty period of the equipment), crypto prices stay the same, and miner competition stays the same. It also doesn't account for facilities costs, salvage value of the equipment, or the (relatively limited) labor costs of setting up and maintaining the computers.