If you can wait come x-mas you can get them cheap. Amazon seems to be as good a place as anywhere. They are heavy so you want to avoid the shipping cost. If there is any type of SB conference in your area they might be selling them cheap.
I found eastbay to have the best deal when I purchased them. Signed up for their silver level which was cheaper than shipping costs and they were delivered in 2 days. You can usually find 20% coupons for eastbay online.
Last year there was a sale on amazon and they were $60 dozen! Someone posted the link on here at the time. I am not sure if it happens every year or not but I bought a dozen and would love to get some wiffles for half the price.