Ask HN: Is there a cheap option to get a trusted IP for sending emails?

Initially, I tried running an email server along with their site on Digital Ocean but Microsoft's (Outlook, Hotmail) filters were sending everything to spam despite SPF, DKIM, and DMARC. Changing IP on DO and waiting for a few weeks to build up the reputation didn't help either. I also had compatibility difficulties like some ancient government server in Guatemala dropping emails because of encoding problems caused by Spanish accents.

We switched to a free MailGun account for routing and SMTP (all org members are using Gmail) and it worked for almost a year. But last month the shared IP on MailGun was blacklisted by Microsoft and lots of emails to Outlook/Hotmail addresses were dropped.

MailGun's dedicated IP is $59/mo which is a significant cost for a six-person organization based in South America. Is there any cheaper ($5-20/mo) option that can help with email redirection and delivery? They send only a hundred or two monthly.

(We are aware of free G Suite for non-profits but it requires migrating everything from personal Google accounts to G Suite accounts, which is really hard.)