In your updatePrice() function you get the number of hours out of the dropdown menu, but the maximum possible number of hours is 12.5. If you select several extras and a really large house, the number of hours becomes larger than the maximum possible at the dropdown, so it renders a wrong price.
This is the line that is causing trouble, you can either add more options to the dropdown or create a variable that stores the number of hours and it can either be changed through a dropdown change, or a change in cleaning service options (size, extras, etc):
var hours = parseFloat($("#num_hours_dropdown :selected").val());