[John Metric]

Since you are somewhere between a drag race and an endurance race, I developed this chart to show the cost per kW versus cost per kWH for our brand. In addition, we just got back some endurance testing from a University testing lab for the Hyperloop pod contest. They were very impressed with the low cell heating at 300A continuous. Cell heating will probably be your issue. The car batteries will be somewhere down below the 25C line. Those lines pretty much indicate the resistance per Ahr. I^2R. These new cells can dump at nearly continuous rating without exceeding upper temp limit until empty. In fact we have some new military released tech 125/250C cells coming in for testing. I am going to have to add another series of dots. We only really offer the 75C and the 100C

 

[Yabert]

I certainly don't discharge my Chevy Volt pack at more than 600A for only 1-2 seconds at time (crazy speed reached fast in a Smart fortwo), but I do this few time a day since 4 years now.

Maybe a chevy Volt battery first gen can be a first attemps for you considering his low cost.
Here some data on 15C discharge: http://www.diyelectriccar.com/forums/showthread.php/power-capability-chevy-volt-battery-109698.html