There are very few things needed:
- 6mm dowel. I bought a 2.4m length for £1.68. Cut to about six inch lengths, that's enough for 16 files.
- Sandpaper. A pack of 10 sheets cost me 89p, and I only used one sheet to make the set.
- PVA glue and masking tape - both from "stock".
That's it. Sixteen files for less than 20p each.