Sorry, I should have thought about posting a link in the first place. Here it is.
http://cgi.ebay.com/ws/eBayISAPI.dll...:X:RTQ:US:1123
At $578 delivered, that's $28.90/AH which was the best I could find at the time I was looking. You also have to consider they do NOT include a charger. I bought one from ping for $52 delivered so my total cost per AH is $31.50. That's still a good price per AH I think.
Using Dewalt 36V batteries for example, which I would dearly love to, are closer to $100/AH.
I realize that AH only tells part of the story, and it is an important consideration. The continuous discharge rate is also important, particularly for high power applications. The pack I bought from dy-power is 1.5C or 30A continuous discharge which is over 1KW. Since I'm using a 600W motor and a 30A controller, the pack will meet my needs.