There's a much easier way to do this than collecting all the cash.
Go to the cheat menu in the 'Options' menu of the Conker's Bad Fur Day 'bar'. You'll see a fire imp in front of the fire. Select 'Cheats' and then enter WELDERSBENCH.
This will unlock all chapters and cutscenes. Then go to the last chapter in the 'Chapter Select' menu (I can't believe I have to say this, but to get there, press
), Heist. Select 'The Vault' in the 'Heist' chapter menu. Load it up, and the achievement will unlock after a few seconds.