Have you heard of RetroAnalytics? It's a predictive analytics platform that offers similar features but without the need to be locked into Firebase. https://retroanalytics.io
We charge a monthly fee which is based on the sessions you are getting and then we have a few different tiers. We should have our pricing up on the site in the next few days and we have a 30 day free trial to make sure you are happy with the product, feel free to reach out to me - david at retroanalytics.io.
Disclaimer - I'm the founder :)