Heh. 42mpg isn't so bad then, eh?
You kind of have to be willing to do things like go to the extreme to change your driving techniques, perhaps make some mods on your car, and learn to solder to wire up your own instrumentation. I can't speak for everyone around here, but I can't imagine anyone willing to build one
for you, but I know from building mine that everyone is very supportive and helpful in every step along the way. Be prepared to spend about $50, several hours of research, and several hours of wiring/testing. Maybe an hour of downloading the Arduino software too
Good luck