Wiring

Hello, I recently had a problem. I was getting a jump from a coworker and he had placed the wrong wires on the battery, the positive on the negative, and now the car will not move. The engine starts, but the petele is stuck down and will not go anywhere. The machanic had tried to replace the throttle actuater, but that did not work. He said that it could be the computer or the petele essembaly, or all of the parts together. Am I being taken for a ride, and what should I do because the amount he is talking for this seems to be crazy?