And if mining rigs didn't pay for themselves (where do you think new Bitcoin comes from?), no one would buy them (except other idiot "clinical associate professors").
If you pay normal US utility rates for electricity, you presently can't mine Bitcoin profitably. You're just effectively buying coinage through your power bill, on top of whatever you paid for the mining hardware. As per the article, this just results in slightly discounted heat, and there are better ways of achieving that end.
As to where new Bitcoin comes from, the amount of Bitcoin mined always stays the same regardless of the number of miners participating. The concept of having lots of people all attempting to be lucky enough to find the next block is only what secures the blockchain, with the mining difficulty automatically adjusting itself in response to changes in total network hashrate. Generally, there's also a bit of a human aspect involved as people won't mine when it's not profitable to do so, with the network hashrate dropping in response to declines in Bitcoin's trading value, and miners coming online as the value rises.
The short of it is, the network already is made up of miners willing to eek by at the tiniest sliver of profit imaginable. If you join in, you're fighting for your own slice of a pie that has already been divided down to atoms. Good luck.