The cheapest dumpling spot around Taipei is Ba Fang Yun Ji Dumpling. Usually situated within the neighborhood, which makes it perfect for lunch or dinner. They are known for their dumplings and potstickers that comes in different types: pork, leek, chicken, corn and pork, and kimchi.
Pairing dumplings and potstickers with their tasty noodles will keep you full throughout the day. The Signature Sesame Noodles, Peanut Noodles and Black Sesame Noodles are delicious. I prefer the the Signature Sesame Noodles over the other ones. The taste balances the dumplings when paired together. For just 5NT/dumpling or potsticker and 30NT for the noodles, you can have lunch or dinner for less than 100NT ($3.50).
Ba Fang Yun Ji Dumpling
Various Locations - Greater Taipei