Hi Jason,
I think people will want to help you, but your question is somewhat too generic.
You may have seen this article from Mendix. Via chat it is not that easy to go into the details, but feel free to reach out.
Hello, good day, did you migrate from OutSystems to Mendix?
My company had faced the same issue you describe: We were moved from an unlimited AO plan to a limited plan and at a very large price increase. Even after weeks of negotiations we still ended up with a a 200% price increase for effectively 50% less capacity. We choose Mendix to transition to, and while it has not been an easy migration moving 70 applications over we are nearing the end with a go live date in the coming weeks. In both cases, we have opted for an on premise installation as we already run and amange our own server infastructure. Mendix offered us an incredible onboarding deal which made the transition financially viable, and licensed under a user model with unlimited applications (due to the nature of on-premise installations).
It's hard to give generic advice since there are so many things we learned, but the biggest thing I think is that you need to be aware that with Mendix, every single application is inheretly treated as its own standalone architecture. Sharing data between apps is not easy, and almost always require custom logic to be implemented (despite their claims for OData services supporting this). Depending on your existing catelogue you may need to spend significant time redesigning apps to better work with how Mendix handles things. Speaking from an on-premise point of view, deployments are a major pain point as Mendix offers no out of the box solutions like what OutSystems provided with LifeTime. Everything is a manual process for deployment.