Reporting an overcharging mechanic

My knowledge of cars is minimal, but a series of recent events has caused me to question the integrity of my mechanic. Going through recent service receipts, I am shocked – horrified in fact – about the prices I have been charged for certain replacement parts, parts that I was advised my car required. I am questioning other items on my receipts such as labour and parts supplied, when the mark-up is already up to 200 percent on certain items! In short, even with my limited knowledge, I am rapidly coming to the conclusion that I have been outrageously ripped off. I have lost faith in these people. Is there a regulatory authority for motor mechanics in Victoria? Internet searches have consistently directed me to Consumer Affairs Victoria, but I was wondering if you could possibly suggest another avenue that was more specialized to the motoring industry please?