I paid £409 for my RNS-E in November 2006, then spent another £60 on extra bits (such as a different antenna, 2007 DVD, removal keys and the adapters) but fitted it myself. Bluetooth kits go for £200-£300 extra, although I don't have it, and mine's never been programmed with VAG-COM either (probably loads of diagnostic errors being thrown up but the RNS-E works fine!).
My total spend is well under £500. The figure of £900 is okay but what you're really paying for is someone's time to fit it, and while I love the RNS-E, it's not worth spending that kind of money in my view.
It is easy to fit as long as you take your time, read all of the guides on the web and have a small degree of DIY ability.