Several years ago, Howard Fosdisk wrote a whitepaper about the Return on Investment of gettng certified. Since Howard is certified in both Oracle and DB2, he was able to do a price comparison between the two programs. I can no longer find the whitepaper on the internet, so you'll have to take my word for it that the conclusion was that it is much cheaper to get certified in DB2, but the benefits are equal to Oracle.
This week I read an interesting article in InfoWorld, Oracle hikes certification testing fees: "The cost of a MySQL Certified Associate exam is said to have more than doubled under the new pricing." Some of the proctored Oracle tests appear to be $195 per take in emerging countries. You can see the blog entry from Oracle's certification team for more details.
The IBM DB2 exams are typically $200 per take in the US and $100 in emerging countries.
For more discussion on the Benefits of Getting certifed... see my previous blog entries.