If you have access to a *nix box, then I'd recommend giving PostgreSQL a try. It's free, feature rich, tries to adhere to standards, and is dependable. I am currently using PostGres now for my company's intranet which has over 300,000 records.
Then again I haven't worked with DB2 or Oracle since I've never had the budget for something like that, but for only 25,000 records I'd say that might be overkill.
my 2 cents,
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