For the popular planes, I don't think there's any question that the kit can cost you more (but not much more), particularly if you include the cost of all your tools and all the extra parts you have lying around.

That means building is no longer a financial decision. It was nice when there was also a financial benefit, but builders love creating things with their own hands. Myself, I'd probably go weird if I had to go an entire winter without a project on the building board.