If you want some ideas for efficient drivetrains, look here:
Kinetic Vehicles
That said, I don't think you will find a much more efficient drivetrain than what's in the Insight now. Mine does get a real-world 70 mpg, and that's driving up & down the mountains, and heading out on the occasional Nevada dirt road...
And I'd still be interested in that $1800 Insight, just for spare parts, or as a donor for a Locost...