I was in Sears the other night getting a new band for my band saw and stumbled across their Electric Caulk gun so I bugged a salesman to bring a battery so that I could see it in action. It was priced at $39.95
At full speed I think it would empty a tube in about 45 seconds. It was interesting to watch it start in slow speed as the motor ran fast for a brief bit of time before slowing down.
It runs at 19.2 volt but I image that driving the motor directly with 12 volt would generate decent speed.
Oh yeah it has a rack and pinion drive system.
They also had a little electric air compressor and a spiral saw on the same foot print.