Ben , if you want to buy the car then get an independant garage not related to the sale to change it for you, get a quote and try to knock it off the price or close to it. also the warranty is worth **** in my humble opinion mate, they are trying to give you minimal peace of mind, knock another 100 off and take it without their warranty too. put this towards the cam belt change.
but am seriously considering it better than a new engine, which in the end would probably cost me what the car is actually worth. Good luck anyway.