Free editions, real ones
Running SQL Server on your own machine, and what it costs
SQL Server runs on Linux as well as Windows, so a Microsoft database no longer means a Windows licence on top. On a VPS you get the parts shared database hosting keeps from you: root access, control of the firewall, your own memory rather than a slice of somebody's pool, and the freedom to tune the instance for the way your application queries it.
On licensing, plainly. We supply the server and Microsoft supplies the database, and two of their editions cost nothing. Developer edition gives you the complete feature set free for development and testing, which covers most staging environments outright. Express edition is free to run in production with a cap on the size of each database, which is enough for a great many applications. If you need Standard or Enterprise, that licence comes from Microsoft or a reseller rather than from us, and it installs here the same way.