Can you elaborate on the pricing difference?
Unless it's for some fringe feature, building your business on OpenAI is probably a considerable (financial) risk in the future.
Say you're building on top of llama and Facebook decides not to update it any more or change the licensing terms (again). Say you're building on some other "open source" model and that project dies.
At least you can keep running the existing model rather than getting locked out over night. That's definitely much better. At least it's survivable. But you would still have to find alternatives and review/scrap all your custom prompts.
EDIT** im sorry that was gpt3.5 - with gpt4 it would be 1000 requests before I broke even at 180$