http://www.badmintoncentral.com/forums/showthread.php?t=22705 2U is about $40 cheaper than 3U, most of them are SP version.
Try Inskysport in Mongkok where you can get a Ti10 with strings for HK$730. I am not sure he will sell it for HK$700 without strings but there is no harm in trying.
The last time I checked with Tung he quoted HKD680 without string. At that time the going rate was HKD650.
Its located at Fa Yuen Street. For orientation, Emmy sports is located at one end of the street while Inskysport is located at a office building on the other end of the street. On ground floor of the building, there are many flower shops open during the day but closed at night. There is also a betting centre next to the building. Have fun Cheers