Hi Archi,
I think that your only chance of finding a totally rust free eleven year old Disco is to buy a Japanese import. There are companies who specialise in this. Try algysautos.com for a start, if they no longer do Disco's they probably know who does. I seem to remember that a 99/2000 Disco with around 70000 miles on the clock was about ?5500-?6500. These were one owner high spec Disco's with no rust as they had spent all there time in a nice warm climate. Never off roaded either as they were bought as "posh" cars by the Japanese. The import company takes care of all the paperwork required to register the car in the UK. If someone advertises an eleven year old rust free Disco which has been in the UK all of it's life take a very close look underneath, especially the rear floor area. If it's all rust free then you will have witnessed another miracle of Christmas!!!
Good hunting.