Not rude, it's a fair comment/ question.
The cost is estimated high, however, if we are able to build it for the cost we expect then that estimate will be closer to the $6k mark. And for the gas mileage, depending on how heavy your foot is, can be very minimally effected if at all. You'll still be able to maintain the 29mph hwy because you will be out of boost during cruising. In some cases, turbos have even been known to increase gas mileage slightly due to their ability to increase the efficiency of the engine.