The licensing cost for SQL Server have increased over the years and limiting some of security features to the top tier sucks ass in this environment, but the training, documentation, knowledge sharing and community is better than any other technical community, closed or open sourced that I have found.

Compared to MySQL, sure. But that's like comparing a spade to digger: both can make a hole in the ground, but you'll want the digger to do some real work.

It doesn't compare as well to Postgres - but the better tooling may well make it worth the $10k in licence fees. That's a month of engineer time in maintenance.

SQL Server's cheap for what you get when compared to the commercial competition. Informix is pretty much dead (and had horrible tooling). Oracle is even more expensive. And compared to Oracle, Microsoft look like angels. Ingres is a bit of a joke.

The big expensive MSSQL licences also include some pretty nifty BI tools, including decent implementations of data mining algorithms.