DB2 is free up to something like eight gig of memory usage. I don't understand why people are so wedded to MySQL and Postgres now that DB2 and Oracle have free and very cheap versions.
I can't speak to DB2, but I am really sick of the weird complexity of Oracle. It's power comes at a fairly high cost of complexity, whatever the pricing structure looks like.
It sure is mired in complexity. I am an Oracle programmer by day and once you put it under load there are some pile of bugs that start to show up! That said, Oracle can do so e amazing work, if you have people on hand who can make it do it!