In my area, the average monthly rent for a two bedroom apartment is $1500/month, or $18,000 per year. If you maxed out substitute teaching, teaching every day you could? That would bring in about $45k/year. And the job comes with no health insurance, retirement, or other benefits. On days you don’t work, you don’t get paid. Full time teaching positions do have benefits and pay better, but those require more extensive licensing.

You could earn a subsistence living substituting where I’m located, especially if you got roommates. But it’s not a long-term viable career if you want to have any hope of home ownership, retirement, etc. A great option for those in transition, but not a career.