BARE (not bear) root fruit trees are cheaper because the nursery can save a lot of money in many ways: (1) no container and soil, (2) minimum shipping weight, (3) minimum shipping size, (4) close to zero in maitenances, (5) extra long shipping time ( no expedite needed).
Since the trees are in dormant state in winter, nursery just bundle them together like a bundle of dead twigs and ship to distributors or customers.( Some nurseries put the root in damp saw dust to protect the root). Bare root fruit trees are available for a short period of time at the end of the cold weather only.
They are the same regular fruit trees you buy later in container, in spring or summer at higher cost. Only winter-dormant trees are available as bare root, not all.