Here's little secret about a local restaurant on Prague airport grounds.
When you walk out the terminal, walk straight thru the parking lot (pass the car rental garage) there is an administrative building. It it directly accross from teminal. Actually this building has the Thrifty Car Rental office on the ground floor, so I guess a shuttle runs there as well. walk in go up the escalator, turn left (actually a u-turn) at the windows of the building that are facing the airport turn right the restaurant/ buffet (self-service) has a interantional rest. sign outside (knive & fork). Should be the only buffet in the building.

Used by airport personnel, always plenty of free space inside though.
Price comparision, beer in the terminal cost 80CZK for a large & 60 for a small. In the restaurnt you pay the local price of 20 CZK for a 1/2 liter. As for food, alwasy some goulash, hot soup & I believe pizza too.

Much better than the cafetieria in the terminal for about 1/4 of the price.