The cost to build a mile of road can vary due to what type of road is being built and where the road is being built.
But to build a undivided 2 lane road in a rural area it costs from $2 million to $3 million dollars per mile of road built.
In Urban areas to build a mile of road costs from $3 million to $5 million dollars to construct one mile of road.
Road construction is very costly and it's usually much cheaper to maintain and repair a road than it is to build a new road.