How about going as Vanilla Ice - think fluro trackies, lots of bling, sidewides caps....
Its a pretty broad range - maybe make insect costumes out of bin bags (black bin bags and yellow electrical tape - instant bee!) buy wings from the $2 shop, black tights / leggings.....
You could go as your favourite lollie / chocolate bar - paint up some cardboard boxes / use wrapping paper....
Good Luck.....let us see pics!!