Welcome along.
I don't know a lot about the astra's but I can say this.
My first service was at Northcity holden. for a minor service. (Fluid change safety inspection etc) they charged $1115. Later on I found they hadn't changed any of the coolant, brake fluid etc. Went through consumer affairs, and unfortunately it ended up at a dead end. As car yards such as these can charge whatever they wanted, and there wasn't enough proof to say they hadn't performed the service stated. Holden headquarters in Melbourne only cared about the Recall notice not being performed on the vehicle. For that we were given a written apology, and that was it. Not even a reschedule for the recall to be performed.
So my 2 cents. Buy your parts from autovaux.co.uk. Generally 50-75% cheaper than buying from a stealership. Even with shipping! Don't bother with Holden in Perth when it comes to servicing. You are much better off going to a trusted local mechanic.
EDIT: How much are they asking for the Astra?