I would look for a supplier of Gel Cel or Sealed Lead Acid batteries in the local phone directory. The batteries are used in emergency lighting, computer power backUPS, and even hospital equipment. The suppliers of these batteries can set you up with a nice little charger.

The ESC would be run in parallel.
The leads from the battery would be split three ways.
pPsitive and negative leads each split three ways. One lead to each Speed control, and
then each ESC will run one motor.

From the Reciever, the Throttle lead would be split three ways to the three ESC.

If you are running only the ESCs and steering,
Be sure to leave only one BEC connected, or, Disconnect all the BEC(switches on the ESC)
and use a seperate battery pack.

If you are running alot of accessories from the reciever, disconnect all the BEC and run
a separte battery pack. BEC are not rated to run much more than two servos under load.