You completely disregarded equating the RNG values for breaking down items. There are multiple silks/leather/stone yet only one type per item in a chest. This material is valued based upon the item level and rarity. 10k was a gross UNDER-estimate in it's entirety if you are not allowed to mix and match mats.
No, rares and uniques generally give 2 types per item, while runes give one of each three types per rune. You'll pull between 5 and 8 mats per large chest. My original claim of 1.5 mats per item might be off by .1, or .2 over the long run, but regardless...
Simplifying here
There is a 75% chance of a low level item slot in a drop from a chest. That's based on a 15 out of 20 RNG roll.
Of that drop you have a 12.5% chance of dropping an item based on weapons/runes/accessories which converts to a 33% chance to drop either a silk/leather/stone based on 3 mat types.
Then you have multiple low level mats in each category...
You see, it probably costs closer to 50,000 than to 10k
...you're looking at it completely wrong. If you have 4+ of all the cloths, 9+ of all the leathers, and 9+ of all the metals, then it doesn't matter which specific item drops of any of the three categories. Any one of them will give you the necessary amount of one of your categories. I find it hard to imagine that most people who have played any reasonable amount of time, or more, won't have dozens of each crafting material, with the more common types numbering 100+.
Like I said, the argument that 10/10/5 is too little, too much, or just right, is NOT what I'm arguing. The miscalculation of gold per mats that scene_cachet, and now you, are using is what I am addressing. In that, you are both wrong.
For what it's worth, I've found the payout of dragon runs to be rather poor, even based on my more forgiving calculations. So, I tend to agree that the payouts should be bumped upwards, or the cost per gong hammer to be dropped.