Like clothes, it depends on several factors. A complete pair of glasses with lenses and frames can run you between $100 to $500. The factors that determine the price are the type of frame, frame brand, lens material, lens type and coatings. Coatings like no glare or Transitions which turn your glasses into sunglasses cost more. Also the lens type has a substantial impact on price. A singe vision perscription is much cheaper than bi-focals or progressives (no line)
I always thought it was cheaper to order online but it’s actually not really. Warby Parker sells single vision glasses for $100 and progressive (no line bifocals) with lenses for $350. This is about what you would pay in a brick and mortar store. BUT it’s worth having a physical place for break fix support.