The BMW 128i Coupe is one of the best used luxury cars you can buy for under $25,000. It shares its 230-horsepower six-cylinder engine, along with its playful handling, with the larger and costlier 3 Series line (BMW’s coupes have since been renamed the 2 Series and 4 Series, respectively). It&#x27;s used 2012 retail price is $20,125.