"Lord Bolton had the same question for me, Your Grace. It took me a while to sift through the ledgers, but I found out the reason for the wealth. House Stark collects little more than a hundred thousand golden dragons on average per year in tax from its lands and all its sworn vassals. Part of it was in kind-food, iron, lumber or other resources. A tenth went to King's Landing in gold as tax. The cost of maintaining Winterfell and all of its household expenses was rarely more than forty thousand gold dragons per year. All the leftover materials were sold for profit."