Not sure. If the Flash image output is $30/M [1] then that's pretty similar to gpt-image-1 costs. So a faster and better model perhaps but not really cheaper?
[1] https://developers.googleblog.com/en/introducing-gemini-2-5-...
Since I can't edit, it seems like Flash image is about 23% (4 cents vs 17 cents) of the cost of Openai gpt-image-1, if you're putting an image and prompt in and getting out, say, a 1024x1024 generated image. With the quicker production time that makes it interesting. Expecting Openai to respond at least in terms of pricing, e.g. a flat rate output cap price or something to be comparable.
https://openrouter.ai/google/gemini-2.5-flash-image-preview