Your mother's maiden name

re: cost of obtaining mother's maiden name.

And how secure is "mom's maiden name" as a password for obtaining sensitive information over the phone?

Not very. Birth records and marriage records tend to be public record. Organizations that do genealogical research tend to have this data around, although they don't always make it easy to get data on the living. On the other hand, most organizations I've dealt with that use it just use it as a password field. You can just pretend that the person on the other end of the line is asking "What is your password?" rather than the standard question. Eric