Bricklink and the Lego Replacement Parts service.

Through Bricklink, you can "Part out a set" and get a full inventory of an official set.

This lists all the parts in a set which you can then Copy and Paste into Excel via Notepad. (Or, I could link to a basic version of my work.)

You can then add all the parts into a Wanted List and then go and Shop by Wanted List.

Prices vary wildly so I am having to balance availability vs new/used vs alternatives vs price vs shipping.

I reckon I can to it for around £600-700........