On average, the cost of meals per person in cities like Lhasa, Gyantse, and Shigatse would be about 10 to 15 $ USD. but in the restaurant along the road, and in the remote places, the average cost for the meal would be 5 – 10 $ USD. but in the Kailash region, the average cost per meals would be more expensive than in any town. The average cost for a meal in the Kailash region would be about 15-20 $ USD.
But the above state price could differ base on the region of your visit and your travel time in Tibet.