Many other elements were unified in 3eD&D, as Clerics, Wizards, and other “full spellcasters” advanced at the same progression from spell levels 1 to 9. The kits of 2eAD&Dwere replaced by “prestige classes,” specialized classes that had specific requirements of feats, skills, proficiencie...
I’d say that’s an argument for the value of soul coins actually being different and just there not being an exact system made by Wizards who’d rather leave artistic interpretation to individual DMs. I believe this is from the traveling Bazaar of Avernus which has a specific character...