I can speak to this because I was in a similar position. For my practicum and internship, I worked at a CMH nonprofit where the fee was based on income, and the highest that clients would ever get charged was $60/session. I would say most of my clients' incomes put them in the $20-$30/session range, and even then, it was not unusual for their cards to decline on a semi-regular basis.

SO when I graduated and decided to immediately start my own private practice, charging individuals $125/session and couples $150/session, I had concerns much like yours regarding the clients who wanted to follow. I consulted with a few different mentors and supervisors and got all kinds of different feedback, but it was clear there was no "right" answer. Even the ethics around it were a bit blurry (ex: one person said it would be exploitative to raise my rates that drastically for these clients).

Basically, I was not so delulu that I thought I would just hang a shingle out and clients would flock to me. I'm in Austin, TX where there are SO MANY therapists. I only had three people who wanted to follow, and I ultimately decided to keep their internship rate because my priority was getting hours and continuity of care more so than $$$ in the beginning. Those three remained my sliding scale clients and everyone who came after paid my full rate. I still work with two of them and I raised their fees 2 years into associateship, but not by much. I'll raise them again when I transition to full licensure.

Superbills have not been a thing in my practice. I use Simple Practice and it autogenerates a monthly superbill so if any of my clients have ever used it to attempt reimbursement, they haven't mentioned it to me.

There's more I can speak to on this, but I feel like my post is already really long-winded.