Depends how you look at it really and whether that's a fixed quote or an estimate. As said there are a couple of possible pain in the arse possibilities. I know from bleeding the brakes on my '99, the bleed nipples on the front calipers loosened easily, but both rear ones only just managed to loosen, so will he replace the cylinders if it goes bad in that price? He'll have to do a double bleed of all 4 brakes, so there will be a reasonable cost in fluid. Having said that, if the parts and fluid come in at £100, he's got £200 to play with after VAT. Dunno what the hourly rate is, but you would think he's got some to spare in there.
If you haven't had the pads changed for a while, it might be worth getting them done at the same time. Shoes will add a little to the job as the drums will have to come off, but probably worth doing, even if just to make sure the pins are in decent condition.
As with a lot of these things where the garage bill is questioned. Its not rocket science, you could spend a day to do it yourself and save enough for a cheap week in Benidorm! I'm no ninja mechanic, but I spent the best part of a day replacing the ABS modulator on mine and the car drove and, more importantly, stopped, afterwards. I had to take the headlight out, which means taking the bumper off as well and its an awkward position leading to fluid everywhere - the hoses should be OK to change (he said having never changed them!). Get yourself one of those cheap "1 man brake bleeding kits" and its a doddle (if the rear nipples loosen!).