> and you can't self-hosted email because sender reputation is too important in business.

You can self-host and use a delivery service for outgoing.

> I think what it would take to escape SaaS is to go back to paper filing

Why not self-hosted alternatives?

> Manually backing-up everything probably costs more in external hard drives and time than it saves in SaaS fees.

I find that hard to believe. Even cloud backup services are not that expensive.