CJam, 20 bytes (or 27 bytes * 0.75 = 20.25)
Here is the no bonus version, 20 bytes:
ri:X,2f+{X\b2,-!},N*
Just for fun, here is the bonus version, 27 bytes:
ri:X{X\)b2,-!},1>{)SX2$bN}/
Here is the no bonus version, 20 bytes:
ri:X,2f+{X\b2,-!},N*
Just for fun, here is the bonus version, 27 bytes:
ri:X{X\)b2,-!},1>{)SX2$bN}/