fairly easy, Hardest part probably was making the brackets even then it wasn't that bad.
Cost, Not sure. Can probably be made for £40-50. I used aluminium tube for the main part, Pressure rated PVC could of been used.
I used a 45 degree elbow at the top as the intake would of been slightly facing the sky and I was worried about rain getting in when parked up. If I knew before I could of got a piece of alu with a 45degree joint in from the scrapyard I got it from.