I bought an old New Holland feed mill for $150.00, it had a PTO driven hammer mill, auger to mixing chamber with off loading auger. Mine came with a number of screens that are used to make various sized material.
My intended use differs from yours, I'll be feeding light gauge insulated copper wire into the hammer mill then running to discharged material over a shaker table to separate the copper granules from the insulation.
I may also process my Black Spruce branches though the hammer mill before loading them into the essential oils distillation unit. Bit I'm thinking the pitch will have a tendency to gum things up.
Hog farmers also used hammer mills which were electric motor powered, I one had a 7.5 hp 220 volt mill.