Looks like an expensive robot to me! well in that you could have done something that you really wanted for the same money and have less trouble. Not been tempted to buy a complete kit yet, but I have used a Pololu Zumo chassis and the RP-5 but only because their both tracked bases. I usually use 4 or 6 AA's (Nimh) but have just ordered some Li-ions same size of AA but 3.7v! so only need 2, a little less weight to carry! Buy a L293 and wire it yourself, OK it loses a little power but with 6 x AA you have enough. Get a cheap Arduino expansion shield for buzzers, in/out etc..
If you care to take a look here: www.melsaunders.co.uk
you can see some of my early robots, but here's a couple of pictures.
Hope it helps, regards