what is a transmount replacement and what should it cost. on 2006 Buick Lucerne

Engine maintenance light went on and that is what dealer said I needed

Asked by for the 2006 Buick Lucerne
What light came on? SERVICE ENGINE SOON or OIL CHANGE LIGHT, because there is no light for a bad trans mount. You need to take it to a good ASE certified independant repair shop. The dealer is pulling your leg.