I've contacted several tour operators in Rome. One includes a car & driver, and one includes a car, driver and guide. The former is about 300 euros and the latter is about 500 euros for a day.
I've read a number of favorable reviews of various guides for ROme, but don't have a sense if a "guide" is required in addition to a "driver".
Am I correct in assuming that a "driver" just drives you to the venue and the "guide" accompanies you into the venue?