On the Vectra B 150 SRI the timing chain should not cost anything as they are cover up to six years or sixty thousand miles which ever comes first.
Mine was done f.o.c and the car was eight months out of warranty at the time. The early B engines where American produced and did have a problem with oil starvation to the hydraulic tensenior and the oil spray nozzle for the chain, so vauxhall know there is a problem.
Dont pay money for a noisy chain -- talk to your dealer.