I know some No7 products are really good skincare wise but as you mention prices can be a little steep on a normal (not mumsnet) budget.
Teo things I would emphasise, usually you don’t need the amount of products you see, but maybe 4-5 max.
Usually a good cleanser, 1-2 serums (maybe hydration, or vit C, or whatever) to target specific points in your skin and a very good moisturiser.
I would then add maybe 1 product that you use every now and then (say once or twice weekly) like a peel or scrub or the like if you get the idea.
I would wholeheartedly recommend The Ordinary. Their products are fantastic and are what I would call extremely cheap for what they are.
Then when they run sales they’re crazy cheap.
the bottles are simple, no big marketing or design budgets and price goes towards the ingredients.