In Texas...if you work for a dive shop, you’ll get about $50 per student (for the whole class, not per day) plus commission on the gear you sell to your students. You use the shop’s gear and the annual insurance is cheaper or covered completely by the dive shop.
If you are independent, you need to buy all your own gear, or rent each time, plus you have to pay for your own insurance...but you keep 100% of what the student pays. So if you charge $350 per student, your expenses will be about $150...so you net around $200 per student. That’s not a lot of money, and scuba instructors don’t get rich...but it can be a great side job.
Plus you have to be pretty good at marketing yourself if you’re an independent instructor...and be prepared for all the dive shops in town to hate you.