Hangar On, not bitter but fact of life. Everything is priced in beans nowadays. Even 8 years ago we ordered a special map (civvie) for BBMF to use around Manchester. After they provided it AIDU tried to stick us with a bill.
We refused on two counts. One was they had not given us the price before hand and the other was the RAF equivalent did not have a visual corridor on.
You might be able to get 'free' out of date maps but QRs even specify what happens to these to.
As you say, it is for charity, now have you tried one of the civilian cartographers? They might be prepared to sponsor you and possibly even give you a tasking.