A leather sheath I made for a neighbor to fit a bush knife, which he found abandoned years ago in Mexico.
This is made from one piece of vegetable-tanned cow leather, stitched with waxed hemp cord and treated with olive oil. I also resharpened the knife and treated the handle with oil and wax to help preserve the wood, which had begun to crack.
The thick, stiff leather is wet-formed around the knife, and retains the shape of the handle as it dries. In this way the knife will not fall out of the sheath, even if you hold it upside down and shake it, but it can still be easily drawn and inserted into the sheath.
A similar custom sheath of this type would cost $40-$60, depending on the size and shape of the tool it is made for.