A $12/month droplet is enough. You can get by on a $6/1gb droplet, but I don’t recommend it.
You’ll also need mailgun or similar. Url be a few dollars a month, though they make it hard to find the pay as you go plan.
Dashboard.literatecomputing.com will install it if you’ll give it api keys for mailgun and digital ocean and your domain name. If you want support you can pay for it, but it will do it for free if you join the free trial group.