Here's another couple of places one can get DE from, and pretty decent prices so far that I've found:
http://www.internet-grocer.net/diatome.htm
http://www.groworganic.com/item_PMB105_Diatomaceous_Earth_50_Lb_Bag.html
http://www.internet-grocer.net/diatome.htm
http://www.groworganic.com/item_PMB105_Diatomaceous_Earth_50_Lb_Bag.html