Disregarding the grandfathered free accounts, own domain is $7.20/user/month on gmail, €5/month on Proton. On microsoft that's business tier feature and AFAIK not supported at all on Yahoo.
replyZoho Mail Lite is $1/user/mo when billed annually.
replyhttps://www.zoho.com/mail/zohomail-pricing.html
A few DNS hosting companies still bundle in a few free email mailboxes with registration costs but that is becoming more rare.