to follow up on some of the earlier posts:

there is a federal civil forfeiture statute on the books. The law which is referred to as having not passed supplements the existing law by creating a presumption. The existing law requires essentially only that the police prove by a preponderance (more likely than not) that the cash is from a crime or will be used in a crime. Its controversial because many view it as an end-around your various protections of civil liberties - ie a forfeiture proceeding is equivalent to a criminal proceeding but the accused has less protection.

I don't know if customs has the authority to search outbound or make you answer questions. However, a pitfall to be aware of is that if you consent to a search then the search is valid. If you don't want to comply, ask them "Do I have to (answer your questions/let you search me/etc)?". If they tell you that you have to, then you are not consenting. By not consenting, you preserve your right to have any "evidence" excluded from a trial against you if their search was unlawful in the first place. In contrast, simply refusing or lying is not a good course, and may constitute obstruction. Most likely, they won't give you a straight answer that you have to.