Price is not proportional to focal length. Two lenses can share a similar range and max aperture but differ greatly in cost because of design, age, and features.

In this case, the 28-70mm f/2.8D is an older, discontinued lens, while the 24-70mm f/2.8G is its newer replacement. Newer lenses often cost more because they use updated optical formulas, coatings, and mechanics. The 24-70 also extends wider to 24mm, which is harder to design well than 28mm, and it uses more advanced elements (including more aspherical/ED elements), which are expensive.

Other price factors include build quality, autofocus system, electronic aperture control, coatings, internal design, and expected market demand. A discontinued lens may also sell for less simply because it’s older stock or commonly found used.

So when buying, don’t compare only focal length and f-number. Also consider optical quality, coatings, autofocus behavior, build, compatibility with your camera, age of the design, and whether you’re comparing a current model to an older discontinued one.