Motor mount replacement

it has been suggested that the problem causing the sound coming from my engine might be faulty motor mounts. I checked on line and they run between 60-90 dollars for the parts. i was wondering for a trained mechanic and shop how hard/cost of a job is it to replace motor mounts? How common is it for them to fail?

I never put just mounts in but transmissions were not bad at all. My work was done under warranty so I can provide a look at degree of difficulity but not customer pay pricing.