Beware the "hidden" costs of a Quest though - if you want to power it from the bike you'll need a powered cradle (or a lead from RAM) which are 40-50 pounds. GPSW do a non-powered mounting bundle for about £350.
All in all I think you can get a Quest powered and mounted for about £400, based on the prices at GPSW.
Plus the Garmin cradle that has power and audio..... I got mine from Rainbow for £49 inc postage and that was the cheapest I could find on the net two weeks ago today when I splashed out.