That unloved Discus is mine
Bought from a club and in need of a new coat of paint.

A good Discus should still go for 35k-40k euro with a cobra trailer.

If you are actually asking the question as to how much to insure your glider for, then that is slightly different.
I have mine insured for what it will cost me to replace it. Not what I think it is worth, nor what I paid for it.

Break your glider today, and you need to buy something tomorrow, it might be expensive if you are under-insured.

D-KCUF