About 15 or so years ago people were flogging their .22 Hi-Powers cheap; the European ammo was virtually impossible to find, and lots of owners were non-handloaders. People are collecting this chambering now, and prices are high, if you can find one for sale in decent shape. Ammo is pricey, but is still being made, and bullets and brass are available. I believe you can form the Hi-Power case from .25-35 Winchester; IIRC this is how it was first designed by Arthur Savage et al.
.25-20's are also high in price for good examples, although ammo is still easy to find and fairly cheap. I'm still irritated at my late uncle who had a really cherry '92 in .25-20 he promised to leave me....then forgot and sold it with all his other guns! Some guy in Kenora probably got a great deal on what was to me an heirloom. Grrrr......