Absolutely you shouldn't be leaving the money out in the open, and should probably hide it. You should absolutely NEVER give consent to search your car. You have no idea what a person is capable of until it's too late. I'm not saying the cop will plant something, though it wouldn't be the first time, but you also have NO IDEA what might be in your car accidentally.
http://www.telegraph.co.uk/news/worldnews/northamerica/usa/1...
As for having dangerous mystery items in your car, if you don't regularly hang out with low lifes that seems ridiculously improbable. Drugs and weapons are not going to sneak into your vehicle or luggage. To have "no idea" what's in your car it would have to be cluttered with junk and you'd have to parade people through it on a regular basis, so uh, don't do that.
"Fuck you" is not an appropriate response, but videotaping responses to respectful questions is: "Am I free to go?" "Am I being detained?" "On what grounds am I being detained?" "Can you please tell me the relevant statutes so I can look them up?"