Over a Barrel with this Quiz

My Volkswagen diesel van takes a little oil from time to time. This is normal for a high performance rig like the one we drive around Europe. Sometimes I have to buy a liter (a little less than a quart) of oil at a gas station. It costs a fraction more than at the dealer or at a auto parts store. If I have a former truck driver or other fellow with me who does a lot of driving I like to ask him ‘What do you think this liter of oil costs?’ The guesses start at $3.50.
(They probably think they’re guessing high. This IS Europe after all.) The guesses continue. ‘Is it $5.50? $7.50? Now don’t tell me it’s over $10, that just isn’t possible.’ In fact, it is and more. A little liter of motor oil costs $28 in Germany, Austria and Switzerland.