I agree, but I think there is already a bit of a baseline. Unless we change things pretty drastically Kull (Doc's Character) already uses plate mail, cast out of bronze for some reason, but it's effectively plate mail. He is, however, the captain of the Empire's household guard, so that doesn't mean that this is commonly available gear. In the setting I proposed most plant life is pretty much destroyed, so if we're going with that wood would be an extreme rarity, but again would be available to anyone who has significant funds. Bone, leather and metal are commonly available and metal shards would be the likely currency in this setting, so my estimate is that the technology exists for late medieval arms and armor sans gunpowder weapons as I can't see how they're synthesizing the powder without advanced chemistry equipment or a natural source of saltpeter, but its kind of a meta agreement (assuming that's good with the involved parties) that metal is still very expensive and unless you feel that your character could rationally afford something you shouldn't have it. I'd advise that the baseline start with most any professional warrior being able to afford laminar of varying qualities as leather would still exist for the padding and the plates can be sewn on as you can afford them. Some of the plates would be bone in the beginning, others bronze or iron, and you'd essentially be wearing your wealth on your body, which I like for a kind of post-apocalyptic hedge knight feel, with more noble types having access to chain, brigandine, plate, etc. Thrusting short swords and daggers alongside axes and other cleaving weapons, to include poleweapons if you could afford them would likely be common, as ranged weapons lose a lot of their intrinsic value underground. The sky would be the limit from there, all depending on how wealthy you feel like your gang is.