I feel (or rather felt) your pain.
When my 14 year old boy started we HAD to get his full uniform, including PE stuff, rugby kit etc…, from a single shop.
I specifically mention the rugby kit at it was all Samurai.
The shirts have the school crest on, so you couldn’t substitute with cheaper M&S shirts, and the grey trousers were a particular grey and it was impossible to find alternatives.
To kit him out was, from memory, about £500.
We didn’t have the laptop issue, but we were “encouraged” to set up a monthly DD with a “suggested” minimum of £50 to contribute to the school. I drew the line at this - i don’t pay tax only to top-up the school coffers out of taxed income.