Hi and welcome.
Ok, my experience of skimming brakes.
Take them off and have them lath skimmed, refitted with new pads....lasted about 2 weeks then started to vibrate again.
GTS, HR Owen skimmed them and I was not confident that it would work. They used their wheel mounted system and did all 4 for £240 of which I paid half.
Took about 3hrs and the results were excellent and drove the car for a year till I sold it without issue.
So, wheel mounted skimmers are the way to go but for the life of me I cant understand why you were quoted £800 to do this if Maserati main dealers can do it for so little.