it does sound like the timing chain has snapped 🙁
they should be changed at 100,000 miles according to Vauxhall.
the likely damage will be some bent inlet valves, possibly cracked guides, but as it snapped on start up you may well be lucky 🙂
also the pistons will be slightly marked but should be ok, they get damaged when the chain snaps whilst driving.
repair will be cheaper than a new engine, expect £350 parts + labour