Willy Wonka
Last year my dd told mevshe was going as wonka.I told her she couldn't, but she already had a list ready.All it'll cost is about £25, but I got it for £5 in a charity shop. Also buy it a few sizes too big so they can use it again.
All you need is a plain black blazer,white shirt,black top hat, black trousers(leggings acceptable) and large black shoes. You only need these things, and is a perfect 5 minute job. No hassle, fuss or make up required.
This is a unisex idea!!!
Hope it was helpful!