Oracle is expensive. Other times, however, Oracle is very much value for money.
For example, the cost to host an OracleXE instance in the cloud running Oracle Application Express? well that only depends on who you're paying for your cloud service.
For interest sake, you can check out Oracle's price lists here.
You can also query the database view v$option that enables you to see which costed options have been installed on your database. Most of these require separate licences for production databases.
Apparently Mogens has a great presentation talking Oracle licencing, but due to webinar difficulties we missed out at a Perth conference.
I always remember an (unverified) story about some people who used partitioning on their DB to eke wonderful benefits to their environment, then did a presentation on it at a local conference. Ergo, the Oracle Sales rep had a little chat with them to sort out their licences ;-)
It's all well and good to have a play around with these features in development, or your machine at home - but don't forget to pay your licences... Larry needs another yacht.