Migrating to another email provider might be a pain when it comes to importing older mailbox content, but any of the alternative email providers would be way cheaper in the long run.

I use Protonmail for myself and around 5 others, with close to 10 mailboxes. I highly recommend it. Not sure what's available from them re. importing older mailboxes - I've never done it - but everything I've used jas been fantastic.

Protonmail's cheap too. Less than $50 annually for all that I use, including multi-user VPN.

I've heard good things about Fastmail too, of you're looking for an alternative.