Ok, ok... it was just a suggestion to try to keep the costs down for everyone, at IRP only. FWIW, here's the battery rule from Tamiya:
Sport packs that are readily available at hobby stores are legal as long as they are assembled from the general hobby industry i.e. Orion, Peak, Reedy, Duratrax, Dynamite, Trinity and Hobbico.
Here are a few other links you guys might like or need:
Tamiya 2005 TCS Rules
Built to Win - BMW Mini Building and Setup Guide by David Beale
RCtech Tamiya M03/M04 Mini Cooper Thread
TCF-legal Tamiya Mini Hop-Up List (PDF)