Triple the cost for the same distance
Many people assume that products and services in mainland China will be lower cost than other places, but in my experience, it is not the case. Vegetarian food is definitely cheaper and better quality in Taiwan.
That is not what I am looking at right now though – I am looking at plane ticket prices to go to places in China that are about the same distance from Seoul as Taipei is. The said plane tickets cost 3x as much as plane tickets to Taipei, and they furthermore are on airlines that offer vastly inferior service and accommodations. Then again, it could be some complicated airline pricing. Buying tickets to Taipei, then back to Seoul, then onward to these same mainland Chinese cities only cost about $50US more than buying tickets that only go directly to mainland China from Seoul.
Of course, I want to go someplace new, so I will probably put up with the added cost… and the cost of yet another visa for mainland China to go with it.