You are right, apparently I misremembered and 1 gold dragon = 210 stags. I have checked the currency exchange above with the wiki and both published RPGs.
And mind you, it is WEIRD. The difference between the silver stag and the gold dragon is HUGE. I guess GRRM really is using the modern relative values of silver and gold, instead of the medieval ones.
That means that, if 1 dragon = 1 pound sterling, Brienne paid little more than only a medieval english penny in that tavern, which is about the cost of feeding a servant for a day...That would mean that a gold dragon could be worth even more than a pound sterling, and would be more valuable than any gold coin ever minted in our world.
Edited by Ser Lepus, 24 January 2013 - 01:09 PM.