Today Show compared drug store makeup with high dollar cosmetics. They selected twins - one wore the high cost while the other drug store makeup. Stopping passers by on the street, they asked which twin was wearing expensive makeup. More often than not the twin wearing cheaper cosmetics was chosen.
There's another interesting article on U.S. News which compares Drugstore vs. Designer.
Much of the makeup we buy has a limited shelf life. I can't say I've ever taken much notice of it. There seems to be few problems with using it after the suggested "use by" date, but make sure you don't share makeup with someone.
If you have a favorite expensive cosmetic, make a list of the ingredients and compare with other brands, you may find there is little difference and most use the same manufacturers (just different packaging).
Rimmel used to be the cheapest makeup in the 60s, but since they have changed their name to Rimmel London it's more expensive. However e.l.f. has a great selection at a lower cost.