As mentioned above, the free demo version of Blitz3D may suit you.
Another option may be to create a scripted version of Blitz3D using Blitz3D and the BriskVM2 scripting engine ( http://www.koriolis-fx.com/ ). You could then compile this as a free tool to use in your course. You would need to feature limit it by removing some of the native Blitz functions, to comply with the terms of use for BriskVM2. You could most likely find enough functions to remove without interfering with your teaching course. You could also add some helper functions for common tasks, which would help with BriskVM2 terms of use compliance.
Another option may be to create a scripted version of Blitz3D using Blitz3D and the BriskVM2 scripting engine ( http://www.koriolis-fx.com/ ). You could then compile this as a free tool to use in your course. You would need to feature limit it by removing some of the native Blitz functions, to comply with the terms of use for BriskVM2. You could most likely find enough functions to remove without interfering with your teaching course. You could also add some helper functions for common tasks, which would help with BriskVM2 terms of use compliance.