the kit installed by a pro mechanic is about euro 1800.00, i get 5.5km per litre and little if any performance loss. Since I didn't want to waste my trunk with a huge cylindric tank, I opted for the "dounut" model that basically is in the spare wheel well, that why I moved the battery, I wouldn't want to take the tank out just for a dead battery...
I'll be glad to take some pics and post them.