I think the local shops that sell chops and make keys are pretty much the same. You won’t get screwed. A typical chop, made of stone (sorry… forgot which type… is it marble?.. I can’t tell) will cost a few hundren NT$.
There are many types. One of the most wonderful conversations with a local I had was when I went to buy a chop from this 80-year old man’s store. He talked with me for an hour about the history of Chinese characters and how chops are made. All I can recommend is that you ask for the typical, traditional type that most Taiwanese get. It’ll have the Chinese characters in an ‘old style’ that’s quite different from the way characters are written today.
Is anyone familiar with this? What should he ask for in Chinese?