In Toronto there are several sushi restaurants using expensive iPads as menus, selections are made and sent to the kitchen and billed immediately. These restaurants are popular for serving speed as well are high variety in their menu offerings. The food items are shown in multiple photos, and the quality of the screen translates to a better representation of the true food item in its photos. Low cost tablets of at least Nexus 7 grade would make such systems more ubiquitious by reducing hardware costs even more.
I think that cost is not important in such experimentations. if you attache a cheap tablet to the table then consumers might not feel the real exclusivity that they might feel. Apple products are good for marketing.