Why does price vary so much?

All paint is three things: binder (holds it together), vehicle (carries it to the wall), and pigments (colour + coverage). Higher pigment content = better coverage, richer colour, fewer coats. Binder type matters too — 100% acrylic binders flex, adhere, and last longer than vinyl-acrylic blends. Epoxy coatings use two binders (resin + hardener) which is why they're tougher and more expensive. That's why a $112 gallon of Aura covers in one coat what a $36 primer needs two coats to do. You're paying for pigment and binder, not the can.