The bearing assembly is a one piece unit which is a press fit in the drum and retained by the big circlip. You will have to fit a new bearing if the old one has fallen apart (about £14). A new drum is about £20, set of shoes about £10, rear brake cylinder about £5.
I've just had to do the lot on my 306! Parts for both sides came to £130 in total. If you replace the cylinders you will most probably have to replace the brake pipes too. You will need them made up at 600mm long with the appropriate male ends.
dok
February 2008