Comment by reaperman
$10,000 doesn't seem particularly large. Just a few years ago, I bought an old truck for $12,000 in one hundred dollar bills.
If you're worried about large drug transactions, a kilogram of cocaine would cost around $20,000-40,000 in the USA, and significantly more in Europe (actual wholesale price for bulk purchase, not inflated police figures that price it at $150/gram).
Personally I think one month of apartment rent should not be considered a suspiciously large amount of cash, and it should be fine to buy a car from a friend using actual cash. I really don't see the downside of leaving those things legal without a threat of civil asset forfeiture.
$12,000 is an out of the ordinary large amount of money - that's why you can note it as a special instance. It's certainly not something you keep on yourself every day, right? I'm not arguing that people should be limited in what money they carry, I'm saying there is a normal range of cash, it's not as nebulous as argued.