I have a website (HTML, CSS, JS) which uses Firebase - I would like to integrate a MYSQL database

I have a website that works with Firebase, I would like to save money by minimising the Firebase functions to only login, signup as I use Firebase login system. The rest of the data I would like to configure for a MYSQL database system. I need to reduce the Firebase functions to pretty much 0 mb / month. I upload my site to Github and then host it through Netlify, you will show me how to intergrate my data inputs on my website to MYSQL database, send data to MYSQL and pull data back to the web page depening on logged in Firebase user. Backend needs to be done 99% in MYSQL. If a user is on the webpage and a user send them a message at the moment the Firebase allows me to see the message updating the webpage without refersh in realtime. If MYSQL cannot do this we will keep the realtime features working with the Firebase DB. Only realtime data should (without page refresh) should use firebase and login/ sign up system Bulk of data (99.5%) should be stored in MYSQL for free. I know that Google Firebase allows integration to MYSQL but I think they charge for this / month so it woud be better to do these things separately, they should be separate systems. Data that is not realtime or is old should all be pulled from MYSQL Database.