In terms of coming up with a cheap easy to make foil suitable for learning on, it may be that we have to find ready made products that can do the job as part of an assembly.
This aluminium extrusion has that blunt leading edge which may be more tolerant of changes of direction in water. I notice that windsurf fins with blunt leading edges are less likely to stall or spin-out and easier to recover from spin-out with.http://www.fractal.be/profiles.asp?id=67
This one would be suitable for putting a 20mm diameter stainless steel rod or tube inside. Seems to be made in Belgium.
Its an example of another product that might be of interest.
If we could find aluminium extrusions of the right shape and materials, it could be that they could be welded together to produce a cheap working foil.
There may also be a possibility of using epoxy and glass fibre inside the aluminium extrusions for strengthening and bonding to other components.