Hi, Luis! For ticket prices, click on BUY TICKETS at
www.disneyworld.com. By adding/subtracting days and options, you can see the prices. Prices do not include sales tax and are subject to change at any time.
With a 9 day ticket, you can add 1 more day to make it a 10 day ticket. This will cost only $3. However, if you add "No Expiration" this is where it gets pricey. You must upgrade your entire ticket, not just the remaining days. Here is the breakdown:
9 day adult ticket with Water Park /Hopper = $344
10 day adult ticket with Water Park /Hopper = $347
9 day adult ticket with Water Park /Hopper/
No expiration = $522
10 day adult ticket with Water Park /Hopper/
No expiration = $556
If you are only going to have 2 unused days on a 9 day ticket, to add the No Expiration option and have 2 days of tickets for a future vacation will cost you $89
per day. The decision whether or not to do this is up to you. I always add the No Expiration option to my tickets as we take frequent trips to Disney, using only a day or 2 at a time, so it is worth it to us to add the pricey option. However, if you always take long vacations (5 days + at a time) you are probably better off not adding No Expiration and buying tickets as you go. Ticket upgrades can be made at any ticket window.
I hope I did not confuse you even more! For more details, see a cast member when you arrive at WDW and the ticket options can be reviewed with you. Good luck!