Russ - RNS 510 off ebay are around £1000.
£1,000 !!!!!!!!!!!!!!!!!!!!
WTF is that about?
?
WTF is it about? the fact VW charge £1800, so in fact its good value, saving £800. 
Check the VWnavi for sale forum, thats where I got mine from, for only £700. Also comes with the latest software and firmware, plus quick delivery. Bluetooth can also be added quite easily, as I've done it myself, again there are discussions on vwnavi if you want more info.
Cheers,
Nigel