Any good costume ideas?

My school is having red ribbon week and for Friday we are supposed to wear our Halloween costume. The problem is that I don’t have a costume and all of the costumes in the stores are EXPENSIVE!!!!!!!! So, do you have any ideas on a good costume I could make in 1 week? It has to be appropriate for a Catholic school, though. Here are the rules:
-shoulder must be completely covered
-skirts/pants cannot be more than 2 in. above the knee
-cannot show any cleavage
-everything that needs to be covered HAS to be covered
-if wearing shorts, must have leggings or tights under shorts
-no blood, guts, etc.
-no “weapons” [fake saws, hammers, swords, etc]
-etc., etc., etc.
Oh, and I am a girl. If you need to know more rules, I’ll do my best to tell you. Please HELP!!