it would help if you had a reference. but since I've seen the movie, I'll give some advice where I can.
If I remember right, she has that hidious hawaiian print shirt? yeah, you can find that shirt at any surf store. no luck with that? Hwaiian print isn't too hard to find.
She always wears a vest, right? or maybe I'm a bit fuzzy. but still, vests are easy to make as well. check out thew 99 cent patterns at the fabric store for a good vest pattern, and sew on pockets.
Headbands, also easy.
The boots you an either have custom made, which would run pretty pricey, do them yourself, or go online and buy the closest thing you can find.
You can get good wigs from Coswoxs, Cosplay.coms store.
You can find a pair of shorts for cheap, or make your own
Hope my overall vagueness helps a little
Ivy(Soul Calibur 3 main outfit): 20-30%(half done with the armour)
Sakura con 07
Proud Sakura Con attendee