I frequently toy with the idea of creating a platform like this using Raspberry Pi or some other SBC where every customer gets not only their own database but their own app server and everything else on a small piece of hardware. Due to heavily localized data and application code you can likely get away with the puny hardware and the cost per account is very sensible even with a pretty high spec SBC.
Seems like you could start with containers to test the model out then move to hardware if the economics worked out. A couple SaaS applications I use right now seem like they are operating multi-tenant on raspberry pi.
