how does a oil / filter change cost $85?

i take it to my mech and i bring my own filter and get charged $20 (of course its not synthetic)

i'm not an oil expert so i don't know if the stuff they put is good or bad....if u don't like it change it somewhere else but don't ever go to the place that messed up ever again

i mean they said they mistakenly put the wrong thing but still wanted to charge u to correct it.....please!