I'm just waiting until I've done enought posts to be able to pm, then I'm hoping to get in touch with Eddie-NL or mortygttdi !
I called an outfit called Satnav Systems and learned it costs about £350 for rear (£450 for front if you want), but if you've got the RNS510 I understand you can either get a rear view camera that displays on the screen, or a parking diagram, though this was around the £600 mark!
I got quoted £300 fitted from the VW dealer I'm getting the car from...