Unlimited emails config with Namecheap domain provider
Google charges $6 per user per month, AWS charges by the number of emails sent/received.
Why not go with FREE (within some limitations)?
If you buy a domain from a domain provider which supports email forward for free such as Namecheap. You can have an unlimited number of emails with a considerable number of emails per day.
Firstly, you need to config your setting at the domain provider panel for it to forward emails (from your custom domain) to your mailbox (e.g. Gmail)
Next, register SendGrid API and integrate SendGrid into your Gmail inbox. This enables you to send from Gmail on behalf of your email at the custom domain.
Sendgrid limits you 40,000 mails for 30 days, and 100 emails/day free forever. That is reasonable if you are using email for personal purposes.
Here is how to set up Gmail to send email via SendGrid: