If one of the developers or a more experienced user has some time I'd also like to have this explained!

(Probably I don't have enough to upvote it.)

By taking a look at the source, I think that this could be accomplished with a couple of ways like a discount line item or by implementing your own IProduct(?) with your custom logic for prices but I have no idea if there is a proposed way for this and I haven't seen any examples on how to implement custom pricing or discounts.

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