Since I just used all my small black gems to craft Onyx Dragon last weekend, I've been calculating how much gold it would cost to get past these steps. To skip the steps would cost 20 gold in Chapter 6 (craft return letter) and 135 gold in Chapter 10 (have Archway) for 155 gold. To buy gems in spell shop, it's 150 gold per return letter, for a total of 300 gold since you need 2 for the archway. Then I saw that I could buy TWO letters for 80 gold total to craft the Archway. For me, 80 gold is doable in order to complete these tales if I can't breed, hatch, evolve and trade 2 rares in a short period of time.
Oh wait, I would still need 20 gold to skip Chapter 6 requirement to craft Return Letter. So 100 gold total.