turn your key-locked cupboard into a padlock cupboard and save a lot of money on the lock budget as you can then ask the students / course participants to bring a padlock themselves.
Padlockable Cam Lock # 300R, 90DG, ΓΈ19x20mm, CPL, Cam A04, Straight C / E: 40 mm
if you need to change from a RUKO lock, you need a plastic insert to change with.