Consider a tree. Kew acquires a rare walnut tree that grows in Souther Staffordshire, because they've payed a farmer from Silverdale ₤15 for a cutting he'd managed to pirate and cultivate. Over the course of that tree's lifetime, from sappling to gnarly great-grandad of the garden, over ₤15 per day may be spent on fertilizer, mulch, pruning, mowing -- all that has to go into maintaining a healthy tree. The lifetime cost of the tree is much more than that first 15...
Books aren't simple items. To risk another metaphor, books and their values are fractal. Not just four-dimensional, but not quite 5-dimensional...
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