>>1824303
>tl;dr
>$255 through crystals and coins tab in the shop
>$56 through new deals - obscure umbra and magic candy

See >>1823286
From lv.1 to lv.15 (max) that's:
>35 copies @ 2.96M coins and 126k crystals
Through the shop tab "crystals and coins," buying just the crystals (3 40k crystals package, 1 4k crystals package, and 1 2k crystals package) is about $255 mad expensive for maxing one legendary cookie.
>How about the packages?
Well, there's that new deals "obscure umbra and magic candy" that you can buy about 5 times to max the latest legendary (2nd purchase = 2 legendary potions, 4th purchase = 3 legendary potions) is about $56

I'd rather grind it, or at least meet the minimum of lv.7 (through grinding as well) if it's to meet the update event mode expectations