Ishgard, the Holy See comes with a five cost to bring back artifacts or enchantments, Jidoor, Aristocratic Capital can six mana to mill one foe's half library
It's possible that Hour of Devastation prices are low because the set simply isn't that powerful for Standard and most cards from the set are unlikely to find homes in tier decks, since Energy and Vehicles are still dominating Standard, and Hour of Devastation doesn't interact particularly well with either mechanic
Another spoiler week has come and gone, and with it, another slate of awesome card
So, instead, I give you the best way to go based on your goal: For fun : The free methods are your friend, my friend
If youre interested in other big-money cards, check out our list of the most expensive cards from Modern Horizons 3 or MTG x Assassins Creed