When DD was at school (she stopped wearing uniform in 2016 when she went to sixth form) we were easily paying that. She had to have a specific school coat and that alone cost £80 - if they wore any other coat they were put in isolation. It was a crappy thin thing too with no hood and they weren't allowed to wear hats, scarves or gloves with it. DD's three mile round trip walks to and from school were hellish in winter but there was nothing we could do.
She also had to have two of everything else bought directly from the school. Only school-issue skirts were permitted and they were £30 each. And two polo shirts, two sweatshirts, full PE kit (or kits - separate ones for gym, football, netball, cross country, etc), regulation school rucksack which fell to bits after six months so needed constant replacement...
Added to that football boots, trainers, school shoes and stuff like apron for crafts (again school issue) and tights (you guessed it ...school issue because they were a very specific colour). It was neverending. DH wasn't earning much in those days and we had to forego things like trips/birthday parties to be able to afford the bloody uniform.
According to the school website it's still as strict and of course more expensive. The coat is now £119!
They even had a colour coded system so each year had a specific colour on the school crest on their uniform so items couldn't be handed down from older DC. Dickheads.