Have you tried AI Horde? It’s a free Stable Diffusion service. You can use it without an account and you get the lowest priority, or you can use it with an account to get priority over people who don’t use an account.

You can also use your GPU to contribute to image generation and you get credits for that, people with more credits get higher priority.

But either way, you don’t ever pay for anything and the only thing that changes is how fast your image gets generated (during peak usage it might be a while, but outside that it’s really fast for everyone).

You can use it for example on HordeNG and you can create an account on the AI Horde website.