A123 cells are about 180wh per kg, hes using 20ah 4 at 104 cells in series. so thats about 104 3.7 = 396 volts at 120ah. multiply that together you get 47kwh of energy. These batteries would be around 500lb.

These battery pricing must've came down a lot over the past couple years because this would've cost something like $40k couple years ago, but a quick google for pricing looks like the battery pack he is using can be bought for around $13k pricing source: http://www.a123rc.com/goods-468-Excitingly+Powerful+A+123+20...