my current costs for hand built ply sleepered points, with C&L chairs is about 12 euros a point. Nickel slivered rail, This is for 00-SF track, but 21mm would be no different
The main caution I would advance for 21mm , if done to p4 standards, is the care that must be taken when laying track, thats the issue, I have seen a number of p4 layouts that struggle to get reliable running
of course there is no reason why 21mm track cant be built to EM standards , which will then allow rp25/100 wheels to be used ( albeit with extended back to back ) and you get the visuals of 21mm without the precise engineering tolerances required for p4
I have recently bought A4 sheets if 1,5mm ply and will cut the point timbers using a miniature proxxon table saw, this should save a fair bit of money over the longer run.
dave