ㄴ/은/는가 하면
I looked up the meaning of 는가 하면 and it says ( not only... But also... )
But in this sentence :
- 왜 저렇게 비싼가 하면, 말을 할 수 있거든요.
I think it means (if you wonder I can tell you why it's expensive like that )
Does 는가 하면 have another meaning ?

Question

Answer

ㄴ/은/는가 하면 has two major meanings.

1. not only ... (but also ...)  == ~이기도 하지만 (한편으로는 ... 이기도 하다).  (하다 = 사실이 있다)

- 7월은 행락 인파가 많은가 하면 (한편) 여러 축제도 있어서 즐거운 달이다.
=> July not only has people going on pleasure trips but also offers many festivals, making it a fun month.

2. to answer the question ... == ~ㄴ/은/는가 설명한다면 (하다 = 설명하다)

- 요즘 무슨 영화가 제일 인기인가 하면 [인기냐면], 바로 XXX야.
=> If you wonder which movie is the most popular recently, it is XXX.

- 왜 저렇게 비싼가 하면 [비싸냐면], 말을 할 수 있거든요.
=> If you wonder why it's so expensive, it's because it can talk.  (* your interpretation was off *)

- If you wonder, I can tell you why it's expensive like that.
=> 궁금하시다면 왜 저렇게 비싼지 설명해드릴게요.

The #1 usage is decidedly literary and seldom seen in conversation.

The #2 meaning is often used in speech, but not as much as ~(이)냐면 which is shorter and has the same meaning.