Hi and welcome to the Forum!
gpt-4o-mini is known to consume a significantly higher amount of tokens relative to gpt-4o or other models, making the cost for image processing essentially similar across models.
Here’s a thread from July discussing this in greater detail.
Additionally, as also referenced in the thread, here is an X post by the OpenAI Head of Developer relations on this very point:
In fact, it would currently even be 50% cheaper to process an image with the latest snapshot of gpt-4o-2024-08-06 compared to gpt-4o-mini given its recent price decrease.