Price by guest is selected from Edit/Add property -> Price Settings

Pay by Guest options are

• Extra Price per guest per night in (currency) and check to Allow guests above capacity?

• Check to  Pay by the no of guests (all room prices will NOT be used anymore and billing will be done by guest no only)

Price adjustments for a certain period are done from the same window.

To set custom price click a beginning date and end date (2 clicks) (updated with more options in 1.20)