Setup is rock solid and hasn’t failed me in the last couple years, since I added the secondary server to temporarily queue mails in case the primary goes down. spamd can be a bit inconvenient sometimes (but that’s on purpose) and I have a script to disable it temporarily when I need a quick email.
I have SPF, DKIM and DMARC setup on my DNS too, as well as requires records like A and PTR for my hosts.
As for the cost, I pay 30$/year for the domain, and 10$/month for the 2 servers. Backup is on backblaze and ridiculously cheap for the amount of mails I backup.