It will all boil down to what kind of maintenance is required. A robot for $50k would pay for itself in saved wages in under a year, even less if it collected tips. A lot of smaller diners (Waffle/Huddle/Waddle/etc) typically have super low staffing requirements (line cook + 1 or 2 servers per shift, occasionally more) and could totally use robots due to the simple layout and standardization of the restaurants.
It will all boil down to what kind of maintenance is required. A robot for $50k would pay for itself in saved wages in under a year, even less if it collected tips. A lot of smaller diners (Waffle/Huddle/Waddle/etc) typically have super low staffing requirements (line cook + 1 or 2 servers per shift, occasionally more) and could totally use robots due to the simple layout and standardization of the restaurants.