I mainly buy second-hand with the exception of school uniforms, underwear and shoes.
My DC are junior school age (upper end).
I probably spend no more than £60 per child on second-hand jumpers, t-shirts, pyjamas, shorts, trousers, fleeces etc. In a year. Maybe up to £10 extra per child on a nice outfit for a wedding / special occasion etc. if needed (again second hand).
A single pair of school shoes seems to last each child a full year now. I buy from Clark's / Startrite so they cost about £30-£40 (I try to buy in the sale).
School uniform is about £70 per child (2 x logo jumpers, 3 x logo polo shirts, 2 x trousers or skirts, basic PE kit (t-shirt, joggers, shorts). School socks.
I always buy school coats second hand and never pay more than £10 for a nice warm, waterproof coat that keeps them dry on the walk to school (e.g H&M, Lands End).
Another £100 each to cover a few pairs of trainers, a pair of wellies, walking boots etc. to last a year.
£30 on a few packs of socks, pants and vests. I buy nice decent quality ones that last.
My kids don't have heaps of clothes as I just don't see why it's necessary. Enough for some in the wash, some to wear and some spare.