I buy a 3 foot piece of steel rod from a big box store, cut it half, heat the end with a propane torch, bend 1-1/2" over to form the blade, beat it flat with a three lb. hammer, sharpen it with a grinder and a file and stick a handle on it.
I made one that has the blade on a 45 to the shaft so I can cut comb off walls or ceilings with the same knife and I do not have to hold the tool at a 90 to the surface the comb is on.
The next ones I make will have rectangular handles so I can tell where the blade is by the feel of the handle instead of trying to see into the back of a dark hole.
I paint all my cut out and yard tools bright yellow, makes them easy to spot in the grass.