engine diagnostic and repair estimate

I have a 1999 Dodge Ram 2500 V-10. The in-dash temperature gauge recently started acting up. I took my truck into Southern CDJ for diagnosis and repair. They said I needed to have my thermostat replaced. The service department informed me that a charge that the cost breakdown was $80 for the diagnosis and $350 (+) for the part/labor. Having some mechanical knowledge, I told them that I would come and get my truck. I told the service person that that was a rip-off. The service manager stepped out of his office and knocked of 50% of the diagnosis cost. Whoopee…..Thermostat/gasket from Rock Auto - $20.52 …1 Gal antifreeze Wal-Mart- $7.00…Local Mechanic labor cost - $60.00. Total cost: $87.52.