Least Expensive Convertibles You Can Buy: Audi A5 Cab Definitely good buy. Forget the price - A5 Cabriolet is one of the best convertibles on the market. Well engineered, reasonably quiet with the top down, back seat accommodates adult friends in comfort. Good looking fun to drive. Factor in the price a lot less expensive than BMW's 4-series, though BMW does get a retractable hard top while Audi A5 only cloth.