Guests who are staying at a WDW resort can have their tickets placed on their room keys. If you purchased a package (room + tckets) or if you purchase your tickets when you check in, the tickets will be coded to your room key. If you bought your passes from another source, you can have them coded to your room key by the lobby concierge.
Here's a list of reputable ticketbrokers:
The Official Ticket Center
Dreams Unlimited Tickets
Ticketmania
Undercover Tourist
Discount Orlando Vacation
Maple Leaf Tickets
Compare their prices, including tax and shipping charges. And if you sign up for the
MouseSavers.com Newsletter (which comes out on the 15th of every month), you'll find links in it for even lower ticket prices at one or more of the above ticketbrokers.
In general, 3-day passes are not heavily discounted. However, a couple of the ticketbrokers are offering 3-day tickets with 2 or 3 free bonus days. So make sure that you check all the prices, since their specials can change from week to week.
How do you get that done?
