Thanks for the prompt response. itch.io still not have a workable solution for the pricing weirdness, I assume? (I don't even know if they've even replied to you.)
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I don't know if generated keys are compatible with items of variable price, but maybe that'd be a solution that would work for giving people access to the items through itch.io? (Understand if you don't want to figure the mess out, though, with a support request waiting.)
It honestly hasn't felt like itch.io care much about its users since it came out the Vintage Story dev hadn't been paid their sales in half a year.