A blog post was just released with some explanation about crafting and some of the more interesting details about the actual costs. The article on the official forums: http://us.battle.net/hearthstone/en/...rust-6-20-2013
The most interesting bit, if you allready know how the crafting works and WHY we have the crafting system in HS:
Originally Posted by Blizzard Entertainment
To be honest, these conversion rates scare the hell out of me. Ratios ranging from 1 to 8, all the way to 1 to 4, for the normal cards. 1600 dust for a Legendary, made by disenchanting common cards worth 5, would take you a mindboggeling 320 cards disenchanted!
I knew the crafting system was going to be with bad conversions to keep people playing and buying packs, but this is kinda over the top, I personally feel.
Much will depend on how often we get rare/epic/legendary cards by opening packs in the game, cause they will both take a load of your crafting needs AND provide much needed Arcane Dust if they are cards you do not need.