what I was saying was if you want more than 44-46mpg you're going to have to put some work into it.
I don't really believe in engine swaps. The top 2 hypermilers have engines that came with the car. Even bajoos put a regular motor in instead of the same motor that he had before and could of saved him more gas and still in the top 10.
So don't sweat the custom gears, the custom motor swaps. Work with what you got.
I have also been looking for a place to cut some gears for the 5th gear of my metro. I know that funny looking tandem metro that got 75mpg had a custom 5th gear the guy made himself. I have not been able to find someone willing to do it without a cad drawing of the gears. If you can get a cad drawing of what you want then there are plenty of places willing to cut them for a decent price ($100-$400) depending on how much work needs done. If you have done all you can to get the best mileage out of what you have then custom tall gears are probably the best bet to improve even further. If you are careful putting them in the dealer will never notice them if you have to take it in for warranty work.
I plan on getting a set made for my car as soon as I figure out how and where. I don't want to give up the 145/12 tires on the car they are very cheap to replace.