most big bm's (and mercs/audi's) of this ilk can be picked up for not much cash compared to new due to depreciation and as they are so heavy on fuel they become silly to run if doing big miles but an absolute steal for weekends as you say.

It's not very technical advice but just remember it was originally a £50k+ car and as such maintenance bills if anything major goes wrong could be horrific, but if you're lucky and buy wisely you'll get a bargain you can most likely run for a year or so for very sensible caseh.