Cheapest flight from Taiwan to Hong Kong

Either you plan to go to Hong Kong for traveling or for visa run, the cheapest ticket you can find is usually offered by China airlines- CA (Kaohsiung <-> Hong Kong) or Cebu pacific (Taipei <-> Hong Kong).. Cebu Pacific is a low cost airline. It means in case you want to take more luggage than just cabin handbag/backpack, you would have to pay additional fee. They also don’t offer any meals or drinks for free on board.

With China airlines, you can take 1 cabin and one additional luggage with weight not more than 20kg. CA has many offices in Taiwan, for example in Tainan there is one very close to roundabout Dongmen – Shengli Rd. You can but a ticket in their office, but when purchasing online it is cheaper. You better go to office when you want to change your flight or have any problem or question. 

Airlines flying from/to Taiwan to/from Hong Kong (in order according to usual ticket price starting with the cheapest). 

Airlines' order may vary depending on season as well how much in advance you're buying the ticket. This scheme is valid for flight bought apprx. 3 weeks in advance:

Cebu Pacific: http://www.cebupacificair.com/Pages/default.aspx

China Airlines/Mandarin Airlines*: http://www.china-airlines.com/en/index.htm 

Hong Kong Airlines: http://www.hongkongairlines.com/en_HK/homepage

Dragon Air: http://www.dragonair.com/da/en_INTL/homepage

Cathay Pacific: http://www.cathaypacific.com/cpa/en_INTL/homepage

Eva Air: http://www.evaair.com/html/b2c/english/

*CA operates Mandarin Airlines' flight including.