Without a doubt, the 1960 Mercedes Benz 190b, I bought in London for £15 in 1973. It was a trade-in for a bog-standard Escort and had been brush-painted with house paint. It ran OK, and even though it was petrol, it sounded more like its Diesel sisters. The Yom Kippur War broke out, petrol prices went ballistic, I couldn't afford to fill it up, so would put a gallon or two in at a time. There was a warning light indicating that there was a gallon left in the tank. It seemed to be permanently on... Rather than abandon it in the streets, it was sold to an inebriated Irishman for £45. Cash.