Even though I think this is a horrible, stupid idea that needs to go to idea jail, the 401/404/Gardiner aren't truly paid for because they're all expensive maintenance nightmares.
But they generate tax revenue from gas. They are only expensive because a handful of construction companies share the "competitive" quoting system and nothing is organized, so you get a paving company on one day with $12M of new asphalt, then a drain company comes in and tears up 3 ft strips two weeks later. Just send the bills to the taxpayer.
Boston went and buried their highways...but they are billions over budget, and they did not expect to see maintenance costs so soon. Big disaster, it already looks 50 years old.