LeiaPix is a free app, with no limit to usage as far as I know.

All of this stuff is free or freemium. For Supermeme you have 20 free prompts and in Soundful you can make 10 tracks. After that, you need to purchase their subscription plan, most apps like this are really affordable, like $10/month. If you have a use case for something like this, that is pretty much nothing if you ask me.