There are plenty of endurance races available to anyone who wants to race $500 junkyard relics. There are also some endurance races available to drivers who want to race million-dollar prototypes. But the options are pretty limited for those who want to race something in between, blogs Stephen Cox.  A cavernous gap separates the numerous entry-level $500 series and the high-end Weathertech Sportscar Championship, which offers only four events of six hours or longer. For some time, Nort...