I bought the Alice dress in the World of
Disney store in DTD in February. I think it was $40 or $45. The neck is VERY small- my daughter, who's a petite 3 year old, struggled to get the size S (5-6) over her head. It has a stretchy back, so, it did fit. I didn't want to go any larger because she was already swimming in the S, but I also didn't want to go any smaller b/c I wanted her to be able to wear it for a while.
If you have a Disney Visa, you can get 10% off at the WOD store.
As others have said, the dress is available at other stores- Grand Floridian gift shop on the second floor and England in Epcot.
The costume is very nice. It's a cottony fabric with a with an attached apron. it has "Alice" embroidered on it. The skirt, as my daughter would say, is "super twirly!" and she loves wearing it. The back of the dress (torso area) is a different type of fabric. It's stretchy and I think the backs of most princess dresses are made of the same fabric.
I had a hard time buying this costume-- she owns every princess dress, but I've rarely paid over $15 for each (love the post-Halloween sales!). I just couldn't see paying $40 for Alice, but she LOVED it so much, I just had to buy it!