I don't think school uniform saves me any money at all. It's just that i have to buy pairs of school trousers, polo shirts and jumpers rather than jeans, tshirts and jumpers that don't have the school logo on. Indeed, tshirts and jumpers without the school logo are cheaper, and I pay about the same for jeans/normal trousers as I do for school trousers.
And without school uniform, I wouldn't need to buy school shoes (which only get worn to school). My children would only require one pair of shoes every time their feet grow. And they'd only need one coat too (instead of the school coat and a normal one).
Or the specially branded PE kit, which at DS1's school features both a rugby shirt and a polo shirt (in a different colour to the normal school polo shirt, of course) and two pairs specialised socks (which I've refused to buy and had to fight with the school over).