If J Crew/Banana etc is a little pricy (and IMO the outlets aren't as good as they used to be) look at Target or Kohl's...just don't look in the junior section. You'd be surprised what you can find.
I will say...don't go overboard.
You've got the rest of your life to wear khakis and stiflingly appropriate sweaters. I think part of the problem is that the clothes in the junior section used to be geared to 17 or 18 year olds...now they seem to be aiming for 12 or 13 year old.