I did 540 km for 25€ in my grandpa's Golf mk2 with LPG (autogas)
That is average usage cause LPG-autogas is cheap,it cost half or price of petrol.
Even my Mazda with nearly 140hp for everyday 'drink' 14L of LPG per 100km and that cost less than 7 euro
Most people in 'east' Europe driving on LPG even me but simple you can't compare experience on LPG and petrol.