Hi There,
I believe the tickets are around $70 per person, from what I remember paying last year. The seating is directly across from Cafe Orleans and The French Market...you know where you get the Mickey Mouse beignets? Across from there. Seating selection is chosen by you by waiting in a line until the seating selection opens, and wait your turn to pick seats.
After you reserved them, you go about your park business until firework time. Then, come to the reserved seating area where you waited in line earlier in the day, tell them your name, and they will guide you to your seats and give you the nifty desert box.
It was fun for my family and me when we did it, the dessert boxes were large and had cute little desserts, fruit, crackers, and cheese, and they offered endless drinks. I am planning on doing it again when we go in August if that helps you decide. Call (714) 781-SHOW to buy tickets in advance, they can also give you more info if you want.
Have fun!