G Suite Business Starter is $6/user. Even if you find something viable for, say, $3/user (and I really doubt so), it just not worth the fuss with migration.
And iCloud+ is $1/month for up to 5 users for 5 domains with up to 3 addresses per domain per user.
I haven't gone through the process yet, but it additionally looks like I will need to borrow a Mac or Windows machine to start up iCloud Email. Once it is enabled I should be able to use IMAP or their web client.
That said, if you don't have anyone in your family with an Apple product, this iCloud+ thing may not be right for you.