Just found a military surplus website with some interesting cheap ski bindings for use with regular winter footwear/welted mountaineering boots.
One looks to be like the universal bindings found on the old Karhu Meta/Sweeper skis,
definitely looks heavier than the x-trace bindings found on Altai Hoks:
They also have Ramer Universal AT bindings that work with any mountaineering boot that has a front welt:
They have some other bindings as well, they all look heavy, but they are all pretty cheap for experimenting with hacks/DIY skishoes.
edit: the Ramers actually look like they might have a different toe attachment than the standard front bar in the Ramer "universal".