Cardsphere usually sets the price around 80-95% of the cards value
It was a lot more exciting than the one that came before it and introduced a big first to the game
Against another blue deck, it often costs just 1 mana to counter a key spell, so its perfect in Izzet Murktide or control lists that try to tempo out their opponent
On the supply side are scalpers, who buy products to resell them immediately for a quick profit, and speculators, who hold sealed products for longer periods, betting their value will appreciate
Using played/damaged cards is perfectly acceptable in a lot of groups, especially for rarer cards that are now twenty years old and exceedingly difficult to find in near mint condition
We know during Antiquities that Urzas an inventor, and we know he has workshops as referenced in the flavor text of Urzas Chalice