I have a collection of them! They're fantastic.
Best place to buy one is generally in person because then you can pick out placement. For example, some designs wind up with "headless" characters or awkward cutoff images. For example, this pic from google shows a TON of headless princesses:
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Whereas, in person you can pick out exactly how you like it such as my Sketch Taylor tote with the perfectly centered Cinderella Castle:
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Pricing in all locations in the park will be the same. You can find them in all four parks, deluxe resort gift shops and Disney Springs. The biggest selection is usually the Co-Op in Disney Springs. You can also use the Shop Disney Parks App to find where a specific style is in stock.
The Disneystore.com website does NOT give AP discount, but the Shop Disney Parks App and in store do.
Yes, you can use multiple gift cards on one bag purchase.
Sometimes, certain patterns go on clearance and will show up at the Disney outlet stores. There are two in Orlando. The Premium Outlet on Vineland is one exit past Disney Springs (exit 68) right off I-4:
http://www.premiumoutlets.com/outlet/orlando-vineland The other is on International Drive:
http://www.premiumoutlets.com/outlet/orlando-international/stores
There's no guarantee there will be Disney Dooneys available at any given point in time, but if you have a car and/or a little extra time, it might not hurt to check. There are also several Disney Dooney groups on facebook which help alrter people to when things show up at the outlets and allow for buying/selling/trading. One of my favorites is
https://www.facebook.com/groups/234094570021776/
And, because I love them, here's my collection!
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Show off yours when you get it! (And be prepared to get sucked in! LOL)