They have 2 styles, each of which have 3 sizes. There is the brown leather one, and the ivory colorful sketch one. Not sure on dimensions, but it looked about the same as my retro DLR bag. I know in that design, the cross body was $170 before tax. Guessing the bigger at $225ish.
Just got back from Aulani. I spent the whole trip resisting buying one of the sketch bags. The crossbody was $175. The tote was $245. They were sold at both stores. Also, the wristlets were $70. There was a much bigger bag - it was a satchel style. Dont' know the price.
No idea on the dimensions other than to say the crossbodies were "typical" and the tote was the same as the medium sketch tote you can get at the parks. It tucks right under your arm when worn over the shoulder.
I can't speak for what Aulani has, but the Disney Store online had the same items they had at WDW. Once in a while they also have 25% off Park merchandise. And if DVC ever fulfills their promise of a free D23 membership, then you'd get a discount buying online as well!