Reading some of the previous comments, the seizure of money information is about 20-30 years outdated. In order to seize money you have to articulate a reasonable cause to believe the money in possession was used specifically for either narcotics, money laundering, or "Ill gotten gains". That includes past history, scales and baggies, pay/owe sheets on you, etc. Nobody will seize John Doe's money if you have $10k in cash and can explain why you have it, such as "I am buying a car and here is the address", or "I just sold my car, and here is the proof of sale document", etc.
The only issue is crossing international borders, either by plane or by driving. The feds and IRS really get concerned with transactions or possession at $10k or more.