Have you taken a look at what CPU mining pays recently? It's a rounding error from zero. A modern Xeon does around 5-10 Mhash/core/s, while ASIC mining is measured in Ghash/s. Leave it on for a year and you'll mine an upper bound of 0.00004-0.00008 BTC/core, according to https://alloscomp.com/bitcoin/calculator (that's even discounting future difficulty increases, so is an optimistic estimate). That's 2-4 cents/core/year. If you have 1000 such cores going full-stop for the year, you'll net... $20-$40.
I think his calculations are off, but his general point is pretty accurate. If you're doing pure CPU mining, even $100k worth of hardware won't generate you that much money per week.
As a pure guess I'm going to assume the actual return you'd see is a few hundred dollars per week.
Depends on the cryptocurrency, he used bitcoin in his follow up to my comment. CPU mining of bitcoin is horrendous (you can get a cheap USB stick that can mine as much as an expensive i7 processor) but other cryptocurrencies were specifically designed to make the gap between GPU and CPU mining much smaller and make ASICs not economically viable.
