Just came across this site...
Just put in what you're after, and you will recieve email / text quotes for the part you require from salvage yards across the country...
May be helpful to some of you
EDIT: Just had some quotes for parts on my E39 528i, seem reasonable to me..
Front driver side ABS sensor £29 inc delivery
Front passenger ABS sensor £31 inc delivery
ABS ECU £55 inc delivery