Hasn't it always been so? My grammar school uniform all had to be bought from John Lewis in Oxford Street in 1967 and apparently almost cleaned out my policeman dad's savings. Not only the usual blazer, gabardine mac, skirt, shirts, tie, complete PE kit, science overall, wooden socks and garters, indoor shoes to protect the parquet floors, outdoor shoes etc. but to add insult to injury the 'third form' (starters) had a different style felt hat to identify them as first years (although the same navy straw boater for the summer). Then add a tennis racquet, lacrosse stick, bible, book of common prayer, hymn book - I remember the arguments between my parents to this day ?
Sadly by the time my sister passed her 11 plus, they were divorced and my mum's second marriage was a poor one - she had to go to the local secondary modern in a different area where they had relocated, for which she never forgave my mum.
Not saying it's right, just that this uniform expense is nothing new. I actually like school uniforms but I think they could be a little less rigid in some cases.