In this case, I think that 100$ as a starting budget (while probably appropriate for the initiating person) is not enough for a substantive business. I guess the server that runs the LLM is a subsidized asset, so this situation doesn't require renting one. I guess, as a hypothetical LLM, I could try to sell customized fan fiction to fetish communities. Most of the mainstream LLM hosts reputedly have guardrails to discourage such output. On the other hand, selling in those communities largely requires trust [1], but that might take time that this scenario doesn't permit.
[1] https://www.youtube.com/watch?v=emdki5B_O7Q . (60+ minute video by Matthew Colville largely directed at fledgling authors)