to be honest, have you looked at the price of teenage sized trousers and skirts?
ds can wear any plain black trousers. We looked at Asda, M%S, Tesco and BHS, (because he is ridiculously fussy about them being comfortable, while at the same time wearing them too low, so them don't fit)
Anyway, primary aged trousers were cheap, tow pairs for £12, but the teenaged sized weren't. They were pretty much £12 a pair across the board.
Ds uniform is pretty good in terms of cost, (blazer £35) and minimum logo (plain black trousers form anywhere, plain white shirts from anywhere etc) but with tie, pe kit, shoes, trainers, football boots etc etc , starting secondary cost us £200-£300.
dd starts in September, they have specific shirts and specific trousers, so it will be more expensive.
The good thing is he is year 8 and we haven't needed to buy any replacements due to growth.
Don't buy 2 jumpers, ds never wears his, because he has blazer and coat, and so doesn't need it.