Cathay Airlines has a promotional rate for specific flights from Taipei to HK for anybody having to go on a short notice visa run. Although the times are restricted to a few flights, you can order the ticket the day of your flight and still get the low rate which is 6237 NT$ (with taxes already included).
cathaypacific.com/cpa/en_TW/ … erssummary
This is only valid for another two weeks though, and then the promo price goes up!