No, you do not have to pay for any expense of your guide and driver. Normally in Shigatse city, Gyantse town, Shelkar town and at Everest base camp, Our guide and drivers are provided with complimentary lodging and breakfast from the local hotels or guest house.
Other than that if you would like to invite your guide and driver for lunch and dinner. You are welcome to do so. but we do encourage you to tip them gratitude before you leave. It will help them a lot.