In my opinion, you will do
In my opinion, you will do better for the environment by just driving your Mazda 6 for another couple of years. I purchased a Prius Prime this year because my old vehicle was a 99 Tahoe with probably 15 MPG, and my commute is 50 miles one way. With $4.00/gallon in California, that Prius saves me at least $100/week. However, in your case the current vehicle actually has a quite decent mileage.