As far as I can tell, the only reason you would need an enhanced licence is if your "production budget" is in excess of 10,000 USD.
Check out their trustpilot rating: https://uk.trustpilot.com/review/www.shutterstock.com
The reviews chime with my experience of them. I don't trust them. How do you prove your budget was less than 10,000 USD? I wouldn't be surprised if you had a hit course, they come after you.
You can read about main source(s) of getting free photos (and other resources) for commercial use here: https://community.udemy.com/t5/First-time-Course-Creation/A-list-of-useful-sources-for-instructors/t...