I think $30 a month is high just for email. I do $5/month now and have been doing this for over 20 years on my domain. (It was more expensive in the past.)
But this is your outgoing email authorized by DKIM... an attacker can use it to take over most of your accounts via Forgot Password flow. I think it is a false economy to have that depend on a shared VM.
You don’t have to store your DKIM keys on the VPS. I keep my signing infrastructure local, and send outgoing mail over a WireGuard tunnel so it looks like it was sent from the VPS.
But this is your outgoing email authorized by DKIM... an attacker can use it to take over most of your accounts via Forgot Password flow. I think it is a false economy to have that depend on a shared VM.