€350 sounds about right to me. i have a 99 opel astra saloon and i have had the timing belt done twice since i got it every 40,000 miles. it is very important to get this done or it can be serious consequences for you're care if you don't.
This is an expensive bit of kit you have to buy the timing belt along with everything else that comes along with it so getting it fitted is quite expensive hope this helps