The longest took about 22 years, for proof I got that off a history book.
quite a lot.
It would depend if you are going to build the road out of coins or bills, and if bills, how high would you want the bills to be stacked. Also depends what kind of bills, 5s, 10s, 20s etc.
$450 millon dollars
About £1.36 maybe lets just say around £2.00