My sister is dragging me along to an anime thing where I have to cosplay Who should I do I dont want to spend do much?

An easy cosplay is to do Dr Who - any of the Doctors make an easy cosplay.

If you want to actually do anime so you will be in theme, pick a jeans and tshirt kind of character with a normal hair color. There are characters in shows like Pokemon that wear a Baseball cap, tshirt, jeans, and gloves. Pick up a PokeBall as an accessory and you are set. You could also pick up a school uniform from Target and pull of any number of characters.