The price being asked is definitely excessive in my opinion, and is in excess of the end value of the watch after restoration.

The Valjoux 7765 movement ended production before 2000, but parts should still be in ready supply, meaning none should need to be custom made. Despite being a manual movement it has fairly extensive parts commonality with the automatic 7750, which is still being made and pretty ubiquitous at that.

A couple of years ago we saw a lot of spare cases and dials floating about (and some being assembled into complete watches), so securing some of the other parts shouldn't be particularly problematic either.

You might be better off taking it to a Heuer specialist and seeing what they can do for you. Whereabouts are you, someone should be able to make a suggestion/recommendation.