We have two Prius, 2003 and 2010, and both exceed the 54 MPG CAFE standard . . . one is nine years old.
The 2010 cost $24,000 and is fully paid off. On the road, we're seeing an annual average of 52 MPG (aka., EPA mileage is less than CAFE.) So we're already there.
Now every car manufacturer has the technology but the problem has been their focus on cheap purchase price led to a series of inefficient cars. It simply transfers the "saved" capital cost to your operating costs . . . your periodic visit to the fuel pump. It is the old adage, pay me now or pay me later.
Bob Wilson