A big part of online games is accumulating virtual wealth. If you're lazy you can buy virtual money with real money, paying to not play the game that you pay for. I did a little study of the price of 1000 gold on 168 US Warcraft servers and came up with some results.
1000 gold costs about $150, although it's over $200 on a fair number of servers. 1000 gold is a lot of gold. It's the price of an epic mount, the most expensive thing many people ever buy. The $150 to buy it is the cost of a year's subscription to WoW. A normal player at level 60 can make 1000 gold in about 50 hours, or about $3 / hour.
There's a lot of variation in the price of gold from server to server. But I can't find any correlation between the price of gold and anything else. Gold costs the same no matter if you're on an old server or new one, have a lot of players or few, or whether you're on a normal or PvP server. I was surprised to find no correlation; maybe the gold-for-dollars market is just really efficient?
I got the price data from IGE and realm ages and populations from the WoW census.
Update: one thing I did not appreciate is how volatile gold prices are. Since writing the above two days ago IGE's median price for 1000 gold went from $153 to $177! I'm collecting more data both in time and from different gold merchants to understand this better.