I just bought some new rear discs and bearings off ebay, cheap and cheerful at £80 including nextday p&p.
Second place price wise was Euro Car parts at £80 + VAT for the lot.
I was going to do the work myself, it is only about an hours labour (apart from the ABS rings) simple stuff tho, any garage can do it.
Renault rear discs, bearings and ABS rings are over £150 for parts alone unfortunately. So with labour you looking close to £250.
It may be worth seeing if you can move the MOT to another day and sort them tommorow. My local ECP had them on the shelf.
Laters,
Donut.