May want to consider setting up a private, on-prem system. That way, you can reliably enforce privacy/GDPR rules. You can also tweak the system to support local training, RAG, MCPs, etc.

This way, the costs can also be controlled. It's some capital investment in local hardware, plus reasonably fixed power/cooling/maintenaance ongoing expenses.

Another way is to use the major AI services for planning/brainstorming specific features, tell it not to implement or touch anything, but to generate a detailed plan for an implementer LLM. Review that plan manually, and when ready, feed it to your local system for implementation and debugging.

This doesn't work if the goal is one-shot vibe-coding. But it works really well for focused feature enhancements, test coverage, and bugfixing.