This understates the cost increase. 3.5 Flash also uses more tokens. artificialanalysis.ai shows these difference to run the whole eval, which I think is more realistic pricing:

Gemini 2.5 flash (27 score): $172 (1.0x)

Gemini 2.5 pro (35 score): $649 (3.8x)

Gemini 3.0 Flash (46 score): $278 (1.6x)

Gemini 3.5 Flash (55 score): $1,552 (9.0x or 2.4x compared to 2.5 pro)

This is a massive price increase... 5.6x compared to Gemini 3.0 Flash