That's not a bad starting point. I agree with JumpHerWho - as long as your base looks expensive, everything else can be much cheaper.
If you're happy with your current foundation and powder, I'd start by getting some good make-up brushes, then your ideal shades of blush and lipstick, then your ideal mascara, then an eyeshadow palette, then start looking at better foundations (unless yours runs out before and needs replacing).
My basics would be:
Moisturiser - Avene Skin Recovery Cream (great base for make-up);
Foundation - Bourjois Healthy Mix;
Powder - No7 Creme Touch Translucent Powder;
Blush - No7 (pink if you've got a white-and-pink complexion, coral if you've got an olive complexion);
Mascara - No7 Lash Adapt (amazing, really buildable but not clumpy, and doesn't go streaky or wear off even if you go out in the rain, doesn't irritate my sensitive eyes and is easy to remove);
Eyeliner - L'oreal Superliner (fantastic applicator, pretty much infallible for me even though I usually struggle with liquid eyeliner, lasts really well and doesn't irritate my sensitive eyes, easy to remove);
Concealer - Benefit Boi-ing (the only Benefit product I like, covers really well and lasts a long time - my pot is getting on for 3 years old and is only 1/5 used);
Lipstick - Une, shade L6 (very natural looking, my-lips-but-better shade that seems to suit everyone), or Carmex if you prefer not to wear lipstick every day;
Eyeshadow - Sleek does some fantastic budget eyeshadow palettes, which can be bought online or from superdrug - I have one called Storm that's pretty good.
Most important IMO is brushes - Real Techniques Expert Face Brush, Stippling Brush and Powder Brush are all fantastic and very low in price considering their quality (can be found on 3 for 2 at Boots sometimes, or for about £10 each online). With those, I can make drugstore foundation look as good as department store (it just won't stay that way for quite as long). The £4 Boots bronzer brush is great for blush, and any cheap eyeshadow brushes (Ecotools does loads of tiny ones for £5) will be fine.
Special occasions:
Foundation - Estee Lauder Doublewear/Doublewear Light (depending on what kind of coverage and finish you're looking for - see an Orange Lady for a colour match and 1 week sample of each);
Eyeshadow - Urban Decay Naked or Naked II palette, depending on your colouring - this will give you lots of versatility, and could make a good birthday present;
Lipstick - one red from MAC (get them to help you find the best one for you).