I have always be interested by those high power Lipo cells for realy short burst of high power (relatively) and I think they can be good for your 10 sec application.
From long time now, I'm interested by those cells: http://www.hobbyking.com/hobbyking/s...&LiPoConfig=10
Theorically, you can discharge those cells in less than a minute and two battery in serie can give you 15-20 Kw of power. Not bad for 7-8 lbs of battery! I think you can try for only 300-400$.
But please take extremely care of the dangerosity of those cells. Putting those one in an insulated metal box is probably a good secure idea.
Oh! and don't forget to charge with balancer charger...