I just made one of those two weeks ago!!
I have always kinda wanted one and had some hard maple left over from my rocking chair so.......
You need to be very precise with you cuts and you don,t have to make the jigs as described if you have a scroll saw for the small parts.
The 1/4' spade bit was my only expence and it was just $2.00 or so. you will also need a bench grinder and hack saw to make the knife. I also used my honing stones to sharpen it.
Now, I need something to use it on and learn how to use it!!
If you have some plans for a marking knife, I would be interested in trying to make a marking knife to go with it.
Rog