Korea, Taiwan and Japan offer digital nomads attractive locations but at prices higher than SE Asia. Due to high prices the interest in these countries has been much less than SE Asia however while they are more expensive they are not as expensive as people might think.
Seoul is perfectly doable for a budget of $2,000 a month. Food and housing are the biggest expenses.
Seoul offers great internet and a wonderful city with a great subway and bus system allowing you to travel around the city easily. It is especially nice for those that enjoy the outdoors or like an active nightlife (though taking advantage of that will increase your budget needs).
The subway is a bit confusing, at first, so keeping this subway map handy might be wise until you get the hang of things.
The shock of sidewalks you can actual walk on and traffic after SE Asia (Singapore is the only place I can recall in SE Asia that was even remotely close to as pedestrian friendly). In Vietnam motorcycles and even cars blow through red lights, barely slowing down (amazingly I saw no accidents though with one such red light runner two trucks had to slam on their brakes to avoid the motorcycle). In Seoul, even cars with a green light that are going to turn across a pedestrian pathway with a walk sign will stop when people are anywhere close to the curb (I have seen nothing like this anywhere – quite a contrast to SE Asia).