"How much is that chair?"
Because the subject in this sentence has been identified, You must use は. We use は when you want to mark the topic (いす) with the property of it (いくら) . People don't use が in these kinds of questions, because the topic has been identified and you just wanted to know more about it.
a) マリアさんは アメリカ人 です。
b) マリアさんが アメリカ人 です。
In example a, you've already known maria, and the アメリカ人 (American) is a trait to know more about Maria, so use は.
In example b, you must put this statement in a particular situation. For example, in a classroom, you wanted to know who is American, so you asked the teacher:
アメリカ は だれですか？ (Who is American?)
And the teacher answered: マリアさんが アメリカ人 です。
As you can see, マリア is an unknown subject, and the only thing you know is her characteristic (アメリカ人), so use が
So: Maria san wa america jin desu ---> Who is Maria Maria san ga america jin desu ---> Who is American
This is just the most basic difference between は and が. You'll find out more complicated grammars in the future. I'm learning Japanese too so my explaination might hard to understand. I'm really sory about that. Go to this link to know more details: https://8020japanese.com/wa-vs-ga/
English doesn't have an equivalent, so to make a prompt that asks for a specfic that/there, it would have to draw out an entire scene for you to place yourself into to reenact. For "that", あー and そー, placments work (あれ, あの, etc), but will change depending on if the object is near the speaker (そー) or not (あー). Typically, DuoLingo has been using "over there" to mean あー placements and just "that" or "there" to mean そー, but either one should be accepted since there isn't any way to make that distinction in English.
Your response is "how much is the chair?" as appose to "that chair". If you started the conversation with "Holy crap, do you see that chair thats super blue?" then "how much is the chair" would be an acceptable follow up since you know what chair you're talking about. If, however, you are standing in a chair warehouse and just said "how much is the chair?", noone would have any idea what you were talking about, and they'd have to ask which and where so they could give you a response.
The purpose here of "その椅子" (そのいす) is to establish which chair you're talking about and should only need to be said once. Afterwards, you could probably refer to it as "the" chair since its understood what you're talking about (unless you're comparing multiple chairs, then you'll need to keep differentiating).
I'm not quite sure why you want to use に in this sentence, so I will try to answer you, but my answer might not address your concerns.
[something] は [question word] ですか
is a very common structure for asking questions in Japanese. The は particle shows you the topic of question. You can think of it like an "=".
椅子はいくらですか。 (isu wa ikura desu ka)
How much is the chair? / the chair = how much?
これは何ですか。 (kore wa nan desu ka)
What is this? / this = what?
彼女は誰ですか。 (kanojo wa dare desu ka)
Who is she? / she = who?
According to Wasabi, the に particle is used to show:
Location of Existence
Result of Change
Object of Verb
Notion of Per
These cases would not make sense for asking a question like this.