AI for building and managing a "fleet" of custom GPTs?

I've been deriving lots of utility from ChatGPT's custom GPT creator, however I'm a little wary about vendor lock-in and don't like the fact that your custom GPTs are pulled the moment you stop paying.

Are there any platforms that are really zoned in on custom GPT creation and designed for users and businesses who want to create quite a lot of them for various purposes?