It will cost you much more than buying standard door ply wood or otherwise.

There is a lot of work flatening the skeleton to equal width and making it straight, only machine can do that with ease. You also got to prepare for the installation of lock.

Ready made are cheaper becasue factory made faster and cheaper in large quantity. Basic economy tells you. If you really like the look of the laminated ply wood just nail and glue to the ready made plywood door will be much cheaper and easier to diy. just my 2 cts