$55 Over at GeoManGear
It has a 3W LED, so should be comparable to the Dinnote 140R. Uses the exact same battery and charger as the other magicshine gear. Over on mtb forums GeoMan said the light head on its own should be available in a few weeks, so just pop in a y cable with your existing magicshine and you're good to go.
Personally, I am a little bit disappointed, but only because I don't own other magicshine gear. I'm using p7 torches, so adding a whole 4 cell battery pack just for a tail light seem excessive, and also kind of expensive. If, however, I was already commuting with the magicshine adding a y cable would be a very attractive and cheap option. Light-head only for the headlight saved you about $40, so light-head only taillight might be VERY cheap (i guess we'll have to wait and see)
Anyway, I'm looking forward to seeing reviews.