need cosplay costume help

[Sapphy]

I'm sorry if this is in the wrong place, but I wasn't sure where to put it.
So, me and some friends are probably going to dress up in different costumes and stuff for my birthday (which, isn't until June, but still), and I was thinking I'm going to make a costume like what Kairi is wearing in this picture: http://2.bp.blogspot.com/_30wkyvBmEfs/THIc9YEEz_I/AAAAAAAAADc/l6YmXh-FdW0/s1600/Kairi-kingdom-hearts-2612637-324-700[1].gif

I've never made a costume, though, so I needed some advice. First off, what kind of fabric would be used? I don't know a whole lot and haven't sewn anything in a while, so I wasn't sure what material would be best.
Then I also wondered where I would get shoes similar to the ones she wears.

How much do these costumes usually cost to make, anyway?

[Ante Bellum]

I'd say just polyester or cotton fabric. Nothing stretchy unless you want it to be. (Stretchy material can be harder to sew.)

For the shoes, they look like sneakers. Maybe get a pair and color them like that?