Engine knocking after no oil in car

I started my jeep one morning and the engine was knocking. I checked the oil and there was none. I put oil in and knocking continued. I had someone look at it and he says I need my oil pump replaced. I wanna know if it's worth it because so many forums say when engines knock hard they need to be replaced to fix the car. This guy is asking $800 to replace the oil pump and is not even sure if it will solve my problem. He said if the oil pump doesn't change the knocking I need a new engine.
Btw when he was looking at it he was playing with stuff under the hood and the engine was not knocking anymore. But when he let go the engine knocked/jumped again.