Dress help please!

[bobbleheadnumberone]

Hi, this is my first post but I'm in desperate need of some help!
I'm going to a dinner dance at the end of this month and I'm kind of stuck over what dress to wear.
I bought one a while back, and although it's nice, it doesn't really blow me away (should a dress do that? Or am I just being picky?), so I've been looking at others.
I'm looking as cheap as possible - £35-40 maximum, perhaps from somewhere like ASOS. I want to get something that suits my figure, I've got a proper hourglass figure so if I wear maxi dresses or similar I tend to just look like like I'm smuggling a potato sack under my clothes. I'm also really pale so have a tendency to look dead!
Essentially I'm just looking for something flattering that's not really expensive - colours, etc aren't that important.
Any help at all will be really gratefully received!