Some magazine did an article about foundation (or base coat as it is now called) and found the cheaper ones are ok but haven't the lasting power of the dearer brands. I tried a Primark once, as a matter of interest as it was only £2.50. It was very light and liquidy but my face didn't drop off!
These days I stick with Laura Mercier base coat as it last all day and is waterproofish when swimming (I swim like a crocodile with face above the water). I think Clarins do nice products and is, I believe, worn by the Queen.
I could rabbit all day on make-up. Sorry.