Salut Simon,
One way would be to use a "week" field which contains the week number. The week number could be calculated from the Reservation Date with simple formatting :
$value = strtotime($fields['reservation_date']->value);
$weeknumber = date("W", $value );
From that field you can use validation to determine high season vs low season to calculate the rates. You can also compare that week number to see if its is already reserved using validation. Using a search type and the
Calendar template, you can present the results. The
code pack would be very useful for the date calculations.
Some things to think about...
Randy