I'm pretty certain that Ipod prices are fixed by Apple, so it really won't matter where you buy it. As for the closest place to Disney, perhaps someone else can help answer that one. The Mall at Millenia is not far away and I'm willing to bet someone there sells them.
Will it be compatible? I can't think of any reason why it wouldn't be.
Steve
P.S. Another interesting possibility - when you arrive in Florida, order one by mail and have it delivered to your hotel. Most computer companies do next day shipping. I always deal with MacMall 1-800-MACMALL (1-800-622-6255). If you plan to do this, call your credit card company before you leave and register the hotel address as an alternate shipping address on your card, otherwise you might encounter a fraud protection problem.