I think all the Zafira engines are all interference engines, if the belt breaks the repair is usually hugely expensive.
Interference means the valves and the pistons are capable of colliding, on an extremely lucky day it just bends a few valve stems (still not a cheap repair especially adding on a belt change), on a bad day it really would not be worth repairing the engine even if it was brand new.
It is normal to replace the water pump at the same time, the pump is cheap, ripping the engine apart to replace it is dear so if the engine is open its good sense to replace the water pump.
I would definitely have the belt done even if the car had only travelled 10 miles, ten years is old in belt terms, it was Vauxhall's guide but most people will recommend changing early due to the expense if it does fail. Price? Anywhere from £200ish at a really cheap place, £300-ish+ at normal, £450-ish+ at a rip-off.
Some of the Zafira's had a timing chain instead of a belt, if it has a chain and its not rattling then it isn't so important as its mileage more than age that wrecks a chain.