I would say that if you spend more money on any one makeup product, that would be foundation and concealer. I LOVE Laura Mercier foundation (I use their powder foundation and secret camoflauge concealor, but I have heard great things about their tinted moisterizer). People compliment me on my skin all the time, but my skin is really not that great, it is just that my foundation covers really well and looks so natural. Bobbi Brown is good too, but I prefer Laura Mercier for foundation and Bobbi Brown and Nars for eye shadows and lipstick.
You should buy drugstore brands for mascara, liner, and lip gloss because they are not really any better. Nars or Bobbi Brown eye shadows or lip sticks have more pigments in them, so they stay on longer and have a richer color. MAC has more reasonably price eye shadows and lipsticks that are better than drugstore.