Mickey Ears are available all over...but you can only get them personalized at the Chapeaux, Main StreetUSA at the MK, and I think maybe at Downtown Disney. The hats themselves are approx $6...
I beleive the shop beattyfamily might be thinking of is The Mad Hatter, but I beleive that is in Disneyland. The only place that I can think of in WDW that does the personalization free of charge is at The Chapeau. You can get stuff personalized at the Christmas shop in DTD, but I think they charge for this service.
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