I have read many comments saying Qwen3.5 various ~30B models, Gemma 4 ~30B models and now Qwen3.6 "better than sonnet".

I don't know how large sonnet and opus are but the rumor is 1T and 5T respectively.

You don't have to use the most recent bleeding edge model to succeed. A local FOSS coding agent coupled with a reasonably priced LLM could yield the optimal ROI.