Sonnet in the Claude Code harness is hard to replicate out of the box. That vertical integration is not easily replaceable but by no means impossible...

OpenCode and their Go plan will get you close if you're willing to put in the config work.

For when you do need the larger models Fireworks has a pretty generous 'Pass' that comes out to about $7 a week for some of the larger bleeding edge models.

Other than that Codex's $20 plan is still somewhat valuable though they keep reducing usage. Google's $20 plan will get you some Opus usage in Antigravity and a generous amount of Gemini. Not sure how long that will last as they've been tweaking pricing and planning language recently too.