Anyone seen a simple, plain, long night dress that is cheap?

[Varfalli34]

M&S had a great plain black, spaghetti strap one on sale for four quid and I missed it. Any ideas of where I could find one. I want one for labour (funnily enough the one I wore last time got thrown away) so don't want to spend a lot of cash. I've looked in primark and those types of places but everything is baby doll. I definitely need long long long.