Roughly $3,500 per square foot just for the panel, not including labor and maintenance. If this happens, it'll be on some private tollway, not draining the tight budgets of cities or states.

Obviously going to be an initial concern, but I do believe, with the right financial backing, it will provide more than it will cost. But just like any major project, it will take a serious monetary startup to really make any sort of reasonable headway. With that said, if the Federal Gov't made this project happen, it wouldn't be that difficult to fund, it would just be a matter of diverting road taxes towards the project instead of the current upkeep of American's highway infrastructure (in small increments, of course).