When they built 7km of the A4 highway in the Netherlands it ended up costing about 900 million euros, so that's what I based the numbers on. Not sure what's causing the massive difference. Maybe the 4 million dollars is per lane? Maybe a different construction technique? Cost of lights, safety rails, etc.? Dry soil vs wet soil? Maybe urban vs rural? Bridges? Bridges are insanely expensive, an 800 meter bridge ended up costing 1.2 billion euros.