"Is it expensive to take a taxi there?"
Yes, it is optional. This sentence should be spoken, not used in formal writing. The destination is implied, and the full sentence is 坐出租车去那里贵不贵？
i tried "坐出租车去那里很贵吗？" and was marked incorrect. i think it should be acceptable.
This is where 很 makes a difference: In the question, it does not function as a pure filler word for the adjective 贵. Instead, it means “very” or “really” and poses (slightly) stronger disbelief.
I'm not sure if it should be accepted. The intonation also has a part in it.
How can it be distinguished when it is a pure filler word for an adjective and when it means "very" or "really"?
This word is really hard to explain due to subjective feelings and all sorts of flexible translations. Here is my gross summary:
1) No.1 rule: If the adjective is negated by 不, then 很 is not a filler. Indivisible adjectives which begin with the character 不 are exceptions.
2) If the adjective ends a “(X is) Y” declaration: filler, “very, really” or in-between ;)
3) If the adjective ends a “(Is X) Y?” question: “very, really”
4) If the adjective becomes a modifier preceding a word: “very, really”.
5) Otherwise, 很 is probably not a filler.
It can obscure the lines if we simply want to show that the object is obviously happy, pleasingly beautiful, displeasingly expensive, etc. Polite remarks also do. To me the filler is not pure or the semantic of the sentence structure “subject(+很)+adj.” is not that simple. For example, “那面墙很白。” never means the wall is simply “colored white” but “conspicuously white at first glance (not necessarily snow-white)”. To simply emphasize the color type, people would, for instance, say “那里有一面白色的墙 (there is a white wall; not 很白的墙)” and “那面墙是白色的 (the wall is colored white; not 是很白的)”. So, it is confusing that both 那面墙很白 and 那面墙是白色的 can be translated to “the wall is white” but the nuance is not neglectable sometimes.
I think the 'there' in the English is misleading, especially since it is not required in the reverse translation of this phrase.
Yes. Hopefully people can understand the topic is 去 (to go, to set out), not 去坐出租车 (to take a taxi).
You'd probably be understood but in my experience, "question structures" usually go after whatever you're asking about.
If you say the sentence that way, the meaning of the sentence will change.
When you say "那里坐出租车贵吗" it would mean "Would it be be expensive to take taxi at (implied location)" instead of what the question says.
Since the meaning changes, your sentence is incorrect.
出去出租车贵不贵 also has the same meaning