That is exactly the problem: I do not need to save money on my LLM calls, so any experiment I do along those lines won't really benefit me very much. I'm deeply curious, but not quite enough to put the work in if I don't have a practical need for it.
I'm constantly surprised at how hard it is to find somebody who can show me a demo! That's why I keep on hassling any company that appears to be selling fine-tuning tooling: if you want people to buy your product, giving them a convincing demo feels like it should be table stakes.
An example on how to train (a presumably small) model to call a get_current_weather function: https://platform.openai.com/docs/guides/supervised-fine-tuni...
It's not such a sexy subject, it's mostly done by companies to reduce costs, which is maybe why there is not much written about it.