Sounds like you were paying AVGAS price + taxes, at least given typical petrol prices in EU. At least in Poland, the situation is that if both are without taxe

Sounds like you were paying AVGAS price + taxes, at least given typical petrol prices in EU. At least in Poland, the situation is that if both are without taxes, then AVGAS is more expensive than car petrol. But taxes add enough on top that taxed car petrol is more expensive than untaxed avgas. This meant that non-airclub planes had significant amount of car petrol conversions done, but aircraft that could be fueled through Polish Aero Club didn't bother. At the airfield I learnt to fly gliders, even the utility car (used among other things for dragging winch wire back to start) was fueled with avgas-100ll, except we also modded it with LPG system that was fueled by normal kitchen gas bottle. The hand-pushed grass mower also ran on avgas :D only the winch and old ursus tractor used diesel due to engine type involved.