What is the cheapest transportation to go from Taipei to Keelung (JiuFen)?

Catch the Juifen bus from the Zhongxiao Fuxing MRT station. It goes from just by the top of (I think) Exit 4 (the exit at the north-west corner of the Zhongxiao Fuxing crossroads - check the map in the MRT station, because under the map is a list of bus stops and destinations), outside GNC health shop. It goes approx every 20 minutes, takes an hour and a bit, and the last one home to Taipei from Juifen is at around 9pm.