The eighth-generation Maxima may not be the first car you think of when dreaming up a powerful, four-door conversion – but don’t discount the full-size sedan. KBB estimates that a well-kept, used example should set you back no more than $21,000. There isn’t a huge variety of tuning options, though. But with a theoretical ECU tune, a cold-air intake, and an upgraded exhaust, you could boost the Maxima past its current 300-horsepower (223-kilowatt) output easily.