To initially build a 1 acre pond as a "hole in the ground" is about 10K +/-20% in western NY at current fuel prices.

I hear that pond renovation is ~1/2 that depending on what you need done. If you want to move the dam to both fix the leaks and increase size thereby killing two birds with one stone completely depends on how much soil needs to be moved. Figure $100 an hour for a large machine + operator + fuel.

Bear in mind that to clean much is a large undertaking of patience and planning. You first have to drain the pond and let it dry for a while before being able to excavate it, though you may be able to suck a lot out with a large trash pump and send it someplace else. Then you have to wait for this, that, perfect weather, and then you don't sleep for a while until it is filled.

I would call a few pond/soil guys in your area to get some quotes together. Ask about in your larger garden stores for recommendations, not all pond builders are created equal. Cheap is not equal to a well-done non-leaking pond.

And remember if you use it for swimming, I have found it is much less expensive than getting a good pool + deck + safety + time + chemicals + etc.

Good luck, and keep us posted on your progress.