I would expect to pay around £250 (including labour) to be on the safe side, plus another £70 for the water pump if you want that changed (water pump is recommended since you're 80% of the way there once the belt is off). The timing belt really isn't a bad job to do on these if you've got the knowledge.
Now I'm not insulting your knowledge and I apologise in advance, but I have to ask since customers have made this mistake at our garage before. You are looking at the belt under the big plastic cover? The cover held on with two bolts on top of the engine. It's just we've had people mistaking the auxiliary belt for the timing belt before.