Monroe Charged hundreds of dollars for unauthorized work Waynesburg, Pennsylvania

My car was making a tapping noise. I was told by two knowledgable people I needed a gasket and or a bolt for the manifold. I purchased the gasket prior to going to Monro in order to save money. The mechanic at Monro told me I had a cracked bolt that needed to be replaced. I showed him the gasket I had in case he needed it. Being the exhaust needed to cool off I was given a ride home. When i was taken back to the store, I asked the mechanic if the bill was 300 to 400 dollars which I had been told by others that I would have to pay for parts and repair. The mechanic told me the parts alone cost 1,100.00 dollars. After returning to the store, the manager told me my bill was 1510.00 I told him I couldn't pay that amount, he then asked me what I could pay. I told him the amount others had told me which was 300 to 400 dollars. He then asked me to meet him in the middle at 800.00. I payed him the amount he asked. The mechanic that did the repair spoke with me after I had payed the bill and told me how difficult the job was. I asked him if he replaced the manifold and he said yes because it would need to be replaced in a year or two. I was in shock that I had payed for something that didn't need to be replaced. I was never asked about any of the work/amount that would be charged.