What should a teacher wear for prom?

[Methenyouplus4]

Don't want something too fancy, too expensive but also need to look like I'very made an effort.

Something I could wear again would be great. Size 12. Ideally not more than about £35 (thinking ASOS/ zara/ supermarkets)?

www.debenhams.com/webapp/wcs/stores/servlet/prod_10701_10001_120010817207_-1

www.debenhams.com/webapp/wcs/stores/servlet/prod_10701_10001_007020810960_-1

Sleeveless

www.debenhams.com/webapp/wcs/stores/servlet/prod_10701_10001_120010826760_-1

Size 12 occasion dresses in sale

[[http://www.debenhams.com/webapp/wcs/stores/servlet/Navigate?storeId=10701&langId=-1&catalogId=10001&lid=%2F%2Fproductsuniverse%2Fen_GB%2Fproduct_online%3DY%2Finsearch%3D1%2Fcategories

I usually wear something super pretty from eBay. I try to make sure I don't show any cleavage and the dress is below knee length.

The links below are similar to what I've worn in the past, except I've not paid nearly that much

m.review-australia.com/catalog/product/view/id/23319/s/take-a-chance-maxi-dress/category/4/

<a class="break-all" href="https://www.google.com.au/url?sa=t&source=web&rct=j&url=www.pinupgirlclothing.com/evelyn-dress-yellow-vintage-floral.html&ved=0ahUKEwibw7uKyZ7UAhUixoMKHceYCcIQFggcMAA&usg=AFQjCNEFyafRsIX_ncw2fzDXdfUBQPmIQA&sig2=T0r0lC-hB4TopGXskKQPOw" rel="nofollow" target="_blank">www.google.com.au/url?sa=t&source=web&rct=j&url=www.pinupgirlclothing.com/evelyn-dress-yellow-vintage-floral.html&ved=0ahUKEwibw7uKyZ7UAhUixoMKHceYCcIQFggcMAA&usg=AFQjCNEFyafRsIX_ncw2fzDXdfUBQPmIQA&sig2=T0r0lC-hB4TopGXskKQPOw

I have never been to a prom so I have no idea what teachers wear but in my mind I would wear slim smart black trousers and a black embellished top with heels. It would be beyond embarrassing to be dressed in a similar style to any of the students...