MySQL is one of the most popular database engines on the market,
available in a
Community Edition
which is free of charge.
It provides the same features Microsoft SQL Server, Oracle, and
DB2 offer for the most common database needs (in other words,
you aren't likely to need to pay for one of these more expensive
database engines unless you have very specialized, high
scalability/performance/availability requirements). Best
of all, services like Amazon RDS offer inexpensive MySQL hosting
at a low monthly price. You'll also find most internet
service providers that offer website hosting will include MySQL
databases as part of your package free of charge. Finally,
if you are familiar with MS Access query language, you'll be
well prepared for working with MySQL views (essentially the same
SQL concept).