connected the displayed price to the slider.

main.py

 from kivy.app import App
 from kivy.modules import inspector  # For inspection.
 from kivy.core.window import Window  # For inspection.
-
+from kivy.properties import NumericProperty
 
 class OrderApp(App):
+    total = NumericProperty(0) # in cents
     def build(self):
         inspector.create_inspector(Window, self)  # For inspection (press control-e to toggle).
+    def amount_changed(self):
+        self.total= round(self.root.ids.food.value*100)
+
 
 
 if __name__ == '__main__':

order.kv

@@ -17,7 +17,12 @@ BoxLayout:
             size: self.texture_size
             padding: (sp(12), 0)
         Slider:
+            id: food
+
             range: (0, 100)
+            on_value: app.amount_changed()
+
+
     Label:
-        text: f'Your total is $0.00'
+        text: f' your total is ${app.total /100:.2f}.'
         font_size: sp(24)