I also noticed that the battery packs were not on sale, and even enquired if that was a mistake, and was told that it was not. Maybe I'll check around further since you found a store that had them marked down.
What I have done instead was purchase from Loew's some AA 2500maH (yeah, 2500) Li-lon - 8 pack for 19$. Just going to solder some more together for the robot pack. The connector looks like an easy part to find.
Since the sale, I've grabbed a bunch of stuff, some just because I wanted it
and some because of the shortcomings found in the kit purchased for my son. What I got was this:
Extra metal (two boxes, as it's an expendable item)
Programming kit!
Extra motors/servos (can always make a servo a motor)
Gear kit
Sprocket/chain kits (2)
Omni wheels (2)
crystals
tank tread kit
shaft encoders (2 sets- good for more that just wheels, ie angular positioning)
I passed on the other sensors, as I can make them if necessary.