THE PRIVATE PILOT WAS CONDUCTING A NIGHT APPROACH FOR LANDING IN VFR CONDITIONS. INSPECTION OF THE CRASH SITE BY THE FAA REVEALED THE RIGHT MAIN LANDING GEAR COLLIDED WITH A RUNWAY MARKER LOCATED BETWEEN THE LANDING RUNWAY AND TAXIWAY. THE AIRPLANE REMAINED AIRBORNE FOR ABOUT 300 FEET BEFORE IT CAME TO A COMPLETE STOP IN THE GRASS MEDIUM. THE AIRPLANE SUSTAINED SUBSTANTIAL DAMAGE AND THE PILOT WAS NOT INJURED. THE PILOT STATED UPON LANDING THE RIGHT MAIN LANDING GEAR COLLAPSED AND THE AIRPLANE SLID OFF THE RUNWAY ON TO THE GRASS.