Costs are incredibly low, as I have ~15 low end box-type servers running as check servers interacting with Drupal via a private API, and one DigitalOcean droplet running prod, with a hot backup droplet. Everything was automated via Ansible early on, and I don't have to touch anything except for patching/updating from time to time.
I also have run Hosted Apache Solr for almost double the time, and it actually earns a decent secondary income. Up to about 25 DigitalOcean droplets now, also all managed via Ansible/Jenkins, and it has a few hundred clients (a couple who have been stable clients for over 5 years, and a few very large names that made me realize even a side project can be stable/good enough for 'big companies' to trust them).
I haven't advertised either except for mentions here and there and having them in some of my social media profiles, but I've learned so much from running both—and even turned some of that knowledge into a book that gives decent passive income on top!