Each gold coin is 31.1 grams of 99.5% or purer gold, you would need $712 to buy one today. 800 years ago Gold was around 75% of the price of gold today or around $500 in today's money. This is a little under the GDP per capita of poorly developped nations today so it can be assumed working adults 800 years ago who were taxed one gold coin per year were experiencing a tax rate of between 60%-80%.