4 lanes and a shoulder on each side - 60 feet
1 mile - 5280 feet
316,800 Square Feet
at least 5-8 dollars per sq ft for minimally engineered roads depending on geographic area, concrete prices for that area steel prices, engineering specs blah blah blah.
So at the very least - 2 million just for the paving, not including subgrade work, culverts, drainage, site work, and so on. After all is said and done - I would assume at least 5-10 million a mile. However in union areas at least double that because they have 4-5 people doing the same work that one person does here in Texas. In the north, state taxes are so high because of paying everyone in the union 30 plus dollars an hour to watch other people work.
So geographic area also has a lot to do with it also.