Hello Dan, to achieve this, you need to do a double din conversion. There are quite a few threads available that explain this. Basically, you need a whole new cage new blank buttons, hazard switch, esp switch, card tray ect..Also your climate control unit needs to be changed for a new one(£450), or you could modify your old one to fit as this will be slightly smaller as this drops down further. It is not an easy process but can be done.
I done a conversion for a bloke the other week, took a good few hours to do. PM me your email, and i can send you a link for the conversion. Alternatively, there are a few people who will do it for you at a price including the parts, ie myself (London) or NHN he travels around.
Once this is all done, it is just a matter of getting your rns-e unit and installing and coding it with vcds. Again we can do this. You will also need an rns-e adaption harness and diversity adapter.
All in all, the total cost including double din conversion your rns-e (you can pick up a good one on fleebay for about £450-500 2010 model) will be around £700 if you do it yourself (£1,150 if you buy a new climate control unit).
Hope this helps mate
Hope this helps.