Y1 DD has five summer dresses and three cardis for summer. She has a big brother, though, so gets very, very muddy and grass-stained. She has five white shirts, three cardis and two kilts (yes, kilts) for winter. I will not wash kilts on a daily basis regardless of how much mud they accumulate (a fair bit, as she bikes to school in the rain).
Plus there's all the PE/swimming/football stuff, plus blazer, coat, bags, and endless other stuff. I don't buy optional accessories (gloves, hats, sunhats etc) as they are so ridiculously expensive.
Y3 DS has five shirts, three pairs of trousers, three jumpers, two ties and all the PE/swimming stuff. Plus blazer, coat etc. He has to have a pencil case with fountain pen, pencils, gel pens, etc in it.
I get most uniform second hand. Blazers alone are £100 new!
I think your DH is right, OP.