Was quite a few years ago but I spent £20 on my dress lol it was from a bridal shop and they had a whole rail of bridesmaidy/prom dresses they were trying to get rid of. I bought two dresses, both 20 quid, one was reduced from 275, the other was originally 215. My shoes were £30 from a different bridal shop and my bag was vintage and given to me by my mum. There are ways around spending hundreds of pounds on your proms without compromising on quality. You just have to shop around a little bit.