I think you have to compare it to your alternative which is prob gpt4 in which case its much cheaper?
The real alternative to a finetuned GPT-3.5-turbo is still the base model with a very very complicated system prompt.
> Early tests have shown a fine-tuned version of GPT-3.5 Turbo can match, or even outperform, base GPT-4-level capabilities on certain narrow tasks.
It sounds like it really depends on what you're doing.
[1] https://www.semianalysis.com/p/gpt-4-architecture-infrastruc...