bfwc_booking_cost.php

<?php
/**
 * Apply the standard booking cost as a fixed cost to a booking, regardless of how long the booking is
 */
function prefix_fixed_booking_cost( $booking_cost, $product_id ) {

  $product = wc_get_product( $product_id );
  $booking_cost = floatval( bfwc_get_standard_cost( $product ) );
  return $booking_cost;
	
}
add_filter( 'bfwc_booking_cost', 'prefix_fixed_booking_cost', 10, 2 );