Old files are cheap at boot sales or scrappies. Grind down to shape and temper, then sharpen and mount the handle/scales. Might be able to turn out a nice little nail cleaner to go with it from an old hacksaw blade.
My third and fourth attempts at knifes made from files during lockdown using YouTube videos as a guide and DIY tools.
The files were originally farrier's rasps which I purchased at a car boot for £3 each. I cut the shape out with an angle grinder. finessed it with a domestic sander, and made the holes with a electric drill.
I then made a small holding jig out of wood to cut in the bevels. That was the most time consuming element - about six hours, so the second knife had the bevels cut in with an angle grinder, hence the curved shape.
The handles, or more properly scales are oak, a beam of which I was given a year or so back when an old barn in Norfolk was demolished. The chap I found to saw it into planks reckoned it was at least 200 years old, and by the nails, possibly from a Naval ship.
Fort the second knife, instead of varnishing it I finished it with Danish oil, which gives it a nice rich sheen.
My bench mark was weather they could slice up an onion well, and they seem to. However as they are made from carbon steel, rather than stainless they are prone to discolouration rather quickly and need properly cleaning and drying after use.
About 3 working days effort spread over a couple of weeks for each knife.