Can I use だけ and しか with amounts?

Question

When I was learning how to use だけ and しか, I was told that だけ and しか both means "only". But the latter requires the verb to be in the negative form.

For example:

あの人だけが好きだ。
I only like that person.

これしか買わない。
Only buy this.

But out of all the examples I've seen, だけ and しか are only used with nouns or verbs. I never seen it used with amounts.

For example:

A: これは高いね
A: This is expensive, isn't it?

B: 全然高くない！１００円だけだよ！
B: It's not expensive at all! It's only 100 yen!

Is that correct? Also, can I use it wih other counter words like 一人 and 三つ?

Answer 1

Yes, you can. For example:

二人だけが生き残った。 / Only two people survived.

君が払うのは100円だけでいい。 / You have to pay only 100 yen.

りんごを5個だけ買った。 / I bought only 5 apples.

ここには三人しかいない。 / There are only three people here.

今は500円しか持っていない。 / I have only 500 yen now.

その話を3割しか理解できなかった。 / I could understand only 30% of that story.

But your example sounds unnatural. The better translations are:

たった（の）100円だよ！

100円（だけ）しかかからないよ！

かかるのは100円だけだよ！

I think 100円だけだよ is not enough for us to infer the subject (the price). So in the second and third examples I added that information by the verb かかる (to cost).

In the first example たった means "only; no more than," which is specific to amounts. By using たった instead of だけ/しか, the subject becomes inferable.