Sounds weird I know, but for my 1.9TD Estate, Unipart (via Vauxhall) were cheapest by far for front discs (GBD957) and a bit cheaper for pads (GBP 861 AF). I haven't yet seen the invoice, but a pair of discs were about £34 + VAT (trade) - best elsewhere was around £50.
I've only taken the car for a quick test drive to confirm that all is well so I've no idea if the pads are up to scratch. If I have any problems, I'll soon tell you all, but I don't anticipate any as my Montegos were fitted with Unipart pads in the days when our former Rover dealer did my maintenance.
Interestingly, the discs are stamped "09 2005".