Need help figuring out pricing for no-code ai app generator web service

Hi All, I recently launched a nocode app maker. This app maker allows the tenants to launch their AI profile image generation business similar to ai profile/headshot image generators. I have made it super simple to launch these kinds of website within few clicks. Clients don't need to hire a developer, worry about deployment or integration with different payment providers. All they need to do is buy domain, create a stripe account, fill out some form and launch their website.

I am having problem figuring out pricing for this kind of service. Each profile photo generation is a fixed cost so I need some kind of pay as you go model but also want to charge per month as some cost is involved in maintaining the web service.

Most of the time I see SaaS webapps have 3 level of pricing. My payment model does not fit nicely into this kind of payment structure. I am thinking of just adding 2 payment blocks: One for monthly payment e.g. $99/month another PAYG e.g. $4/job.

Any guidance will be greatly appreciated. Thanks!