How to calculate the room price depending the check in/out dates

I run my small studios webpage
     A costumer needs to rent a room
     i need an easy way to calculate the total price
     depending the check in, check out dates and the type of the room

     two room the one cheap the other one expensive
     the price changes every three months

   for example

   Room 1 price 10 euro per day (jan,feb,mar)
   Room 1 price 20 euro per day (apr,May,Jun,)
   Room 1 price 30 euro per day (July,Aug,Sept)
   Room 1 price 15 euro per day (oct,nov,dec)


   Room 1 price 20 euro per day (jan,feb,mar)
   Room 1 price 30 euro per day (apr,May,Jun)
   Room 1 price 40 euro per day (July,Aug,Sept)
   Room 1 price 25 euro per day (oct,nov,dec)


   Thanks in advance

<select name="room" id="room" >
                                 <option>Select Room</option>
                                 <option>Room 1</option>
                                 <option>Room 2</option>
                                 </select>



                           <input type="text" name="checkin" >

                           <input type="text"  name="checkout" >




                           <p>Total price in euros is:</p>

                           <input type="number" name="Totalamount">