Lupo purchase advice

My friend would like to buy a Lupo. She would spend max. 600€. Actually he should only participate in city trips and therefore consume as little as possible. Actually, I would rather take a diesel, even if it is only 15 000 km a year with it. But in the price range many already have running performances over 100 000km! Is that still acceptable. Does a 3 cylinder petroler last a while? And what about the SDI? Is it recommended. Ithilfe, don’t have a plan from Lupo! Thank you