Ordering Script - Need help

[GladiatoR]

I've just added a paypal script. I've currently got it so whenever someone buys a photo on my website (www.jlphoto.com.au/gallery) that it gives them an option to chose either local pickup or $3.00 postage. It all works fine, adds the 3 bucks to the photo price but how do i make it so it only adds it to one set of photos and not just each individual photo? The code can be found below.

<!--//START 2nd Dropdown List Form -->
           <FONT size="2"><b>3. Select Postage Method</b></font>
           <blockquote>
              <SELECT onchange="ReadForm (this.form, false);">
                                  // values for paypal                  //what your user sees
                    <OPTION value=' Option 1: Posted +3.00 '>    Posted (+ $3.00)</OPTION>
                 <OPTION value=' Option 2: Locl Pickup '>    Local Pickup</OPTION>
              </SELECT> </blockquote>