I'm finding this thread confusing. Why did he say it was a dress?
It's obviously his go-to in his regular habit of trying to make his own pathetic, awkward ego a bit bigger by putting women down: just his well-rehearsed Neanderthal comment to throw without thinking at apparently-confident women. One small step up from "Your Mum" - like 'hilarious' teenagers. If the tag hadn't been visible, he quite probably would still have made the same 'not worth it' comment based on what he 'reckoned' it 'probably' cost.
Rather like Richie in Bottom, and his "That's a smashing blouse you've got on", as something to say to all women, regardless of whether or not they were wearing a blouse. At least, I suppose, Richie was trying to say a nice thing - still not particularly a character to strive to emulate, though!
If he can't tell the difference between dungarees and a dress and also thinks £28 an unspeakably outrageous amount for the main constituent of an outfit, he really isn't worthy of anything more than pity.