Gary
I have a Caterham aeroscreen. I my experience the swap from windscreen to aero takes me about 10-15 minutes. Disconnect the heated screen wires on each side, this is a little awkward but once you know where they are it is quite easy. Remove the wiper arms, they just pull off. Loosen the 4 screen allen bolts. I normally place a blanket on the bonnet to lower the screen onto. Pull the heater wires through the scuttle holes. Lower the screen on to the blanket once the bolts have been removed.
Fitting the aero is then very simple, clip the screen to the centre poppers, and refit the 4 allen bolts the hold the screen down. Job done.
The reverse process takes a bit longer, say 30 mins as it normall takes me some time to line up the allen bolts as the screen seems to require some pushing and pulling to get the holes to line up. This may be just a problem on my car.
So in short it is really fairly easy.
Don't know the costs, ring Caterham.
Nick