The cheapest brake ducting can be sourced from any Home Depot! In the shop-vac section you can buy vacumn hose in 2" and 3" sizes and nozzles to use as a duct. Tie wraps will secure all pieces.

The routing the duct on the right (passenger) side is pretty easy. The routing on the driver's side is a bit trickier with the crank pulley and accessory drives to deal with.