You're biggest issue will be labour if the body has to come out to swap the engine
That's pretty much a certainty given that the 'correct' way to change the cambelts on Disco 3/4 is to take the body off, as one set is on the back of the engine so I'm told. I say 'correct' as apparently the rear cambelt can be changed without taking the body off, but it sounds like a very difficult job getting down the back of the engine and you'd have to wonder at the quality of the job.
Anyway I wouldn't think taking the body off is a major issue to someone who knows what they are doing and who has the right kit for the job. As Mick says you have to be prepared for big bills with these cars, and I believe a cambelt change at a indy specialist costs about a grand! More at the LR stealers no doubt!
The body is designed to be removed, because the timing belt isn't the only job that requires it. It's done with a two post lift.
That said, plenty of garages do the belt job with the body in place, trading ease of fitting for the work involved in removing the body. Also, I believe the rear belts are for the fuel pumps, and don't need to be timed.
£1000 timing belts are nothing new; Renault say that their V6 engines need to be removed for a belt, whereas nobody actually does that.