Folding door mirrors would run into the thousands to have fitted after.
Cruise is under £200
Reverse sensors are under £300 iirc
rns510 is anything between £600-£1200
Ipod connection is about £200 (and not really worth it)
Heated seats will be expensive
Arm rests come up on ebay and i have seen them around £250-£400
If you want to save money, get an aftermarket stereo with ipod connection, tomtom (which has bluetooth for your phone) and a hot water bottle for the seats, the mirrors hardly fold in so dont worry about that, i get out and use my hands
