For those of us haven't been able to purchase a sigil or win one, yet, here's some good news from the Guild Wars site:
Future Update
In order to combat the rising cost of Celestial Sigils and thus allow more people to buy guild halls and experience the guild warfare aspect of the game, we will be substantially increasing the number of Celestial Sigils entering the economy. Starting with this week's update, whenever a team wins a game in the Hall of Heroes, that team will receive three Celestial Sigils instead of one. We will also be making improvements to the trader to allow his prices to more accurately reflect supply and demand within the game.
http://www.guildwars.com/news/gameupdates.html
Hurray!