You can configure a different pricing for each weekday by going to scheduling page > online payment.
You can either enter a percentage or you can check the box absolute value, to add a set amount to the price. Either way the surcharge will be added in the summary of the booking.
In this example the service has a price of 100€, on Saturdays an extra charge of 20% will be added:
Notice: The online payment does not need to be active to be able to use the option to set a different price for each weekday.