Scope of negation in 「カラオケはいちばんお金を使いません。」

Question

I came across this sentence in みんなの日本語　I.

カラオケは　いちばん　お金を　使いません。

I now understand this sentence means:

Karaoke is the cheapest activity. (or Karaoke is the activity that spends least money).

However, I originally thought this sentence meant:

Karaoke is not the most expensive activity.

I now know the second meaning is not the right answer, but if I encounter similar sentences in the future, how can I know the ません negates only the お金を使い, but not the entire いちばんお金を使い?

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「みんなの日本語I」の教科書に、こんな文がありました。

カラオケは　いちばん　お金を　使いません。

これは次のような意味だと理解しています。

Karaoke is the cheapest activity. (or Karaoke is the activity that spends least money).

（訳: カラオケはいちばん安い遊び（活動）です or カラオケはいちばんお金を使わない遊びです）

しかし、はじめに読んだとき、私は次のような意味だと思いました。

Karaoke is not the most expensive activity.

（訳: カラオケはいちばん高い遊びではありません）

今は、これが二番目の意味ではないと知っていますが、もしこれから同じような文章を見た時、「〜ません」が「いちばんお金を使い」全体ではなく、「お金を使い」の部分だけを否定しているということをどう見分けたらよいでしょうか。

Answer 1

Karaoke is the cheapest activity.

"Karaoke" > "カラオケ"
"is" > "です"
"the cheapest" > "最も安い"
"activity" > "遊び"

カラオケは最も安い遊びです。

カラオケは　いちばん　お金を　使いません。
カラオケ(という遊び)は　(他の遊びの中でも)いちばん　お金を　使いません。

All this is the same meaning.
Because,「いちばんお金を使いません」= 「最も安い」

But,

Karaoke is not the most expensive activity.

"Karaoke" > "カラオケ"
"is not" > "ではありません"
"the most expensive" > "最も高い"
"activity" > "遊び"

カラオケは最も高い遊びではありません。

Note:
A:「最も高い遊びではありません」
B:「最も安い遊びです」
A is the meaning that is different from the B.

Note2:
“いちばんXXXです” + “お金を使いません” = “いちばんお金を使いませんです”
“です” was abbreviated.
therefore “いちばんお金を使いません”

Answer 2

The least expensive : いちばん 金を使わない

Not the most expensive : いちばんは 金を使わない

Answer 3

The みんなの日本語 example literally translated reads:
Karaoke uses the least money. [カラオケは一番お金を使いません]
Another way of saying it would be:
カラオケは一番お金のかかるものではありません [Karaoke is not the thing that uses the most money]
To say it in a more straight manner
カラオケは一番高い娯楽ではありません [Karaoke is not the most expensive activity {activity in this case is substituted for the kanji for leisure; 娯楽－ごらく}]
To say the message it as basic and easily as possible
カラオケは一番安い娯楽です [Karaoke is the cheapest activity]
A different way being
カラオケは一番お金がかかりません [Karaoke uses the least amount of money]
It really depends on what situation you are in, how you would like to say it and who you are having to talk to.

EDIT: Sorry, I just re-read the question. I misunderstood the question initially.

To answer how the ません negates only the お金を使い, but not the entire いちばんお金を使い you would look at the sentence structure.

The sentence "カラオケは一番お金を使いません" has the structure [Subject] > [Adjective] > [Topic / Status of subject] > [Quasi-Verb].
The Quasi-Verb interacts only with the secondary subject. Taking the examples of things like ラッシュの電車は一番空いてません [The rush hour train is the least empty (the most not empty)] or 中国に行くために、飛行機は一番時間がかかりません [To get to China, to fly is the quickest (does not use the most time)] you can see this is true in most cases. The ません would reverse the meaning of the verb would it have been a ます - カラオケは一番お金を使います [Karaoke IS the most expensive activity] in much the same way as putting not in front of a verb in general English sentences changes only the meaning of the verb.