School Appropriate (ish) Ariel costume for tween?

I am allowed to wear my halloween costume to school... I am thinking ahead and want to be ariel. Problem is, It needs to be "dress code" appropriate (not show stomach and stuff) if i can find a solution for that-it would be great! I am 5'3"... and I don't want something too expensive... Thanks so much!! I also want to actually look like ariel.. not a random mermaid... Being human ariel would be cool too (i guess) if that is my only option.... My friend might want the same thing for jasmine... Thanks again!