A fairly industry standard rate is around $100-250 per page. A "page" being about 5 panels, so generally that's about $30 per panel, which is probably what I'd charge if I was asked for a "per panel" rate; about $30 USD or £25 GBP kind of area.
At that rate, if I finish three panels a day working just mon-fri, I'm earning £1500, or £18,000, which isn't amazing, so I'd probably want to be completing more panels to make that work out.... but then that's why I don't work full time as a comic artist, but prefer to work part time in edutainment, where I make close to that amount working just two days a week and can draw whatever the hell I want the rest of the time.
Still, it's an amount somebody could live off if they were making more than a few panels a day, and if they had other income streams (like say, a patreon, merch, did regular cons to sell books etc.) or of course if they lived somewhere less expensive than the UK, or had a partner with a steady income.