If the local welding shop can put a sharp knife edge on the backside of the shanks - if the points can be removed. That would be the cheapest (remember, he did not want to spend money on a subsoiler).
I would think he could buy an axle and a few disks with hubs... and mount that under the box blade.
Disks like these:
Coulter Blades
I would think he could buy an axle and a few disks with hubs... and mount that under the box blade.
Disks like these:
Coulter Blades