Sounds like you need 2 things to start with, a new battery and a Central Locking Pump Module.
( it's located under the floor of the trunk on the passenger side in a gray foam container )
You can usually find a working one at salvage yards for around $100-$200.
You can unplug the yellow tube running to the gas door and either suck on it or blow on on it to get the pneumatic plunger to release the gas door. ( a replacement CLPM would also let you unlock the door )