The larger axe is less expensive, because there is less labor involved.
With the tomahawk, I take the axe, which is cast to shape, and modify the shape, re-file the cuts, and re-finish the steel. Same the handle, which I buy, then stain, oil and finish. With the hatchet, I totally modify the shape, cutting the new shape out of the pre-existing handle blank.
To put it another way, I cut the hatchet out of the axe.
Thank you for your interest.
Bob