Nutty, are you sure you need to wear foundation and powder at the same time? I remember reading you're very young...
Anyway, with prices in mind and quality, here it goes:
I'm not an expert but I would say make the most expensive purchase a good concealer for under eyes and blemishes. I'm afraid with this product you get what you pay most of the time. I use YSL Touch Eclat for under my eyes and the odd reddish mark on the face. It does not cover it as such but the skin looks better. There are some green coloured sticks/fluids for covering up spots, Clarins do one and am quite sure most of the others do too, probably even No7. IMO it is best to treat blemishes than cover them up (cannot recommend TeeTree Oil highly enough for spots, or Neutrogena do a spot gel). That's why a very good cleanser suitable for your skin type is essential. You would notice a dramatic improvement in your skin condition. And drinking lots of water (cheaper than buying expensive make-up!). Then you need a reasonable day moisturiser and a very good night moisturiser. I think Olay do pretty good stuff and would also consider NO7 skin care for this. Nivea might be a good one too, not sure about L'oreal as I never heard anyone talk about it. If you have a good skin care routine, you'll find your skin would improve within a month. remember to exfoliate once a week with a very gentle product (look in Boots own plant based products or body shop, don't need to spend a fortune here).
Foundation: don't know much about this but I've heard Lauder's one mentioned earlier is good, Clinique and Prescriptives do one tailor made for you (not cheap though), from looking at magazines, there's an advert for a foundation compared to the feeling of cashmere, can't remember the make but someone here would know, either maybeline or Max factor?? (if I was to try a foundation I would go for that, but that's purely because of advertising).
Powder: no idea, but apparently Lancôme do a very good one (not cheap again)
Mascara: As said before, the best rated affordable is the pink and green one by maybeline
Lipstick: to be honest I don't think it really matters what you buy here, they don't last that long anyway so buy whatever takes your fancy. My personal favourites are by Clinique but have a few which I use regularly from all sorts of places and one of a good quality is from No7 as it happens.
Blusher: no idea. make sure you get someone along to help you choose the colour though as it's a tricky one. I use a powder, but there are lots of solid ones around (like a giant lipstick) which are supposed to be easy to apply.
V. good idea from someone else earlier, do go and have a make-up session at a department store (I think Body shop do them too) but leave your purse at home. Most of them work on commission so they'll tempt you with all sorts of things.
Phew! what a long post again.... To conclude: Touche Eclat the best investment (about£20). And look after your skin first, then see if you really need all the make-up! When do you have time to put it all on? With all the little ones??? Are you some kind of Wonder Woman?!
Happy shopping!