This deck does cost a lot of dust to craft the full fledged deck, however some expensive cards can be replaced.
This deck revolves a lot around getting that early game board control, which, due to the efficient dragon synergies, is not uncommon. When you have early board control you will be able to play your bulkier minions with little risk, such as Ysera or Deathwing, Dragonlord.
Now here is where dragon priest is different from other control decks, you can actually keep one of your bigger dragons (5+ Mana). This is so your dragon synergies will always activate for the beginning turns, in return giving you control. You should only keep one of those big dragons and the rest should be 1-3 mana minions, things like Power Word: Shield might not always be the best seeing their are many more low cost cards that can fill it's place. A good combo to have is Northshire Cleric and Wyrmrest Agent.
Cabal Shadow Priest - Very useful for keeping board control, and don't hold back when you can play it, taking control of any card with it is worth it, even a wisp, ok maybe not a wisp but you get what I'm saying.
Ysera - A solid card to used when you have even the slightest bit of board control, it is out of range for other Priest's Shadow Word: Death and almost all damaging spells. Her stats combined with her effect, which gives you more options for late game and more board control, make this dragon a force to be reckoned with.
Nefarian and Chromaggus are both cards that you most likely have if you are trying to build this deck (from Blackrock Mountain Expansion). They are both good replacements for your high level legendary dragons, however they are much less versatile then Chillmaw and Ysera. I highly suggest that if you can only craft one of these three legendaries, that it is Chillmaw due to its high capability of turning the board around and... well... it's a high level taunt, who doesn't need that.
IMPORTANT- DO NOT replace Deathwing, Dragonlord with Deathwing. Eventhough they have similar names and the same stats, they are COMPLETELY different cards. Seeing as you should have board control on the 10th turn, AND your dragons are still in your hand for synergies, loosing your hand and killing your board will not exactly be ideal. If you lose board control, you have a giant wall of icy death, also known as Chillmaw