@bythewell - There are definitely degrees of formal dress wear and not all of them are going to cost the earth. For one thing, it's perfectly possible to get a some really nice formal dresses from a second hand store. Whenever I've needed something for, say, formal wedding attire, I've hit the thrift stores and almost always found something suitable.
And even if you're buying new, there are plenty of off the rack dresses that would look good and not cost too much. It's the same as anything, there are always going to be the very high end pieces, for people who go to Hollywood red carpet events, and then there are the dresses you can find in an average department store for a few hundred dollars or even less.
Personally, I think people put a little bit too much emphasis on labels, but I do have to admit that often the high end dresses look more like art than clothing and maybe that justifies the price tag.