Commuter car idea

I am entertaining the dream to have a commuter car that would be more fuel efficient, without going deep in debt to purchase some newish hybrid standard model.
So, there are some guys building this (after the "Locost" Ron Champion school):
Bud-jet

Never mind the humorus name. :/
My idea was to build a superlight, simple car with engine converted to run on LPG (about half the price of gasoline, here).
Of course I would need windshield and roof, sometimes it pours over here and winters are very cold.
My estimates place this project consuming like 4kg gas/100kg and would be a great improvement over the Benz.
Any thoughts or ideas?

Quote
Jose Pinto
I am entertaining the dream to have a commuter car that would be more fuel efficient, without going deep in debt to purchase some newish hybrid standard model.
So, there are some guys building this (after the "Locost" Ron Champion school):
Bud-jet

Never mind the humorus name. :/
My idea was to build a superlight, simple car with engine converted to run on LPG (about half the price of gasoline, here).
Of course I would need windshield and roof, sometimes it pours over here and winters are very cold.
My estimates place this project consuming like 4kg gas/100kg and would be a great improvement over the Benz.
Any thoughts or ideas?

Why not just find an older Toyota Yaris, Fitz, Echo...they already get that kind of fuel economy on regular gasoline. Convert it to LPG and it might even do better.
These little cars are quite fun to drive and they have surprizing amout of get up and go!

The Toyotas I like are about my age:
toyota starlet

Those are either rust buckets ore a bit expensive.

LPG conversions don't improve fuel economy (unless the car had injection or carb problems), the gain is the price difference per kWh from gasoline to LPG, is about half the price.

The Benz has set the standard of comfort, economy and handling a bit high, not easy to improve. If only it was newer and had half the km in it... :/