Hello sister! Be sure and stop in the ASA forum to say hello.
It all depends what school you are at - at some larger schools, the members buying new things is the norm (as you will see elsewhere in the Rush forum). For western, you could wear jean miniskirts and t-shirts with bandannas for belts (I totally feel you on the no cowboy hats thing) and have cookout type food.
There are lots of threads on themes for rush - you can do a search or if you look in the recruitment stories portion, some of the rushees talk about what the themes were when they went through. Good luck!!