dendouasisutozitensya dakara, nedan ga takai wake da.

Here, だから means because it is / that’s why and introduces the reason for the conclusion.

In this sentence:

• 電動アシスト自転車だから = because it’s an electric-assist bicycle

So the speaker is saying that the fact it is an electric-assist bike explains the high price.

A key nuance: だから often sounds a little like the speaker is connecting the dots for the listener:

• It’s an electric-assist bicycle, so of course the price is high.

It can sound slightly conversational and explanatory.

わけだ is very important here. It does not just mean reason in a dictionary sense. In this pattern, it means something like:

• that’s why
• it makes sense that
• no wonder
• so that explains it

So:

• 値段が高いわけだ = that explains why the price is high
• or no wonder it’s expensive

This pattern is often used when the speaker reaches a natural conclusion from some information.

So the sentence feels more like:

• It’s an electric-assist bicycle, so that explains why it’s expensive.

not just the flat statement:

• It’s expensive.

Both are possible in different contexts, but が is natural here because the sentence is presenting the price being high as the thing that is explained by the reason.

• 値段が高い focuses on the price is high
• 値段は高い would sound more like as for the price, it is high, often with contrast

Because わけだ often explains a specific fact or conclusion, が works very naturally:

• 電動アシスト自転車だから、値段が高いわけだ。
• Because it’s an electric-assist bicycle, that explains why the price is high.

If you used は, it might suggest contrast, such as:

• the price is high, but maybe something else is not

So が is the more neutral and expected choice here.

高い is the plain dictionary form of the adjective high / expensive and it directly modifies the implied statement:

• 値段が高い = the price is high

You would use 高く when the adjective needs to connect to something else, for example:

• 値段が高くて買えない。
  • The price is high, so I can’t buy it.

But in your sentence, 高い finishes the adjective clause before わけだ:

• 値段が高いわけだ
• it makes sense that the price is high

So 高い is correct.

It is a compound noun meaning electric-assist bicycle.

You can break it down like this:

• 電動 = electric-powered
• アシスト = assist
• 自転車 = bicycle

Together:

• 電動アシスト自転車 = a bicycle with electric assist, usually a pedal-assist bike

Japanese often combines several nouns into one long noun phrase like this. There are no extra particles inside because the whole thing acts as one noun.

Japanese often omits things that are obvious from context.

So this sentence may really imply something like:

• これは電動アシスト自転車だから、値段が高いわけだ。
• Since this is an electric-assist bicycle, no wonder the price is high.

But if everyone already knows what item is being discussed, Japanese usually leaves it out.

This is extremely common. The sentence sounds natural even without an explicit subject.

The final だ is the plain-style copula. In わけだ, it helps complete the explanatory expression.

Compare:

• わけだ = plain style
• わけです = polite style

So this sentence is plain/casual in tone:

• 電動アシスト自転車だから、値段が高いわけだ。

A more polite version would be:

• 電動アシスト自転車だから、値段が高いわけです。

The meaning is basically the same, but わけです sounds more polite or formal.

Yes, but the nuance and structure change a little.

For example:

• 電動アシスト自転車なので、値段が高いわけです。
  • More polite and slightly softer
• 電動アシスト自転車だから、値段が高いわけだ。
  • More conversational/plain

A few notes:

• だから is common in speech and casual explanation
• なので is often a bit more formal or softer
• だからです would usually be used when ending a sentence, not when continuing into another clause

So in your sentence, だから is perfectly natural.

It comes from the same word, but in grammar patterns like わけだ, it acts more like a set expression.

By itself:

• わけ can mean reason
  • わけを説明してください。
  • Please explain the reason.

But in 高いわけだ, it does not literally mean the reason is that it is expensive. Instead, the whole pattern means:

• that explains why it’s expensive
• it makes sense that it’s expensive

So it is better to learn V / adjective + わけだ as one grammar pattern.

Very often, yes. わけだ frequently sounds like the speaker is recognizing or explaining a conclusion.

For example, if someone sees the high price and then learns it is an electric-assist bike, they might say:

• 電動アシスト自転車だから、値段が高いわけだ。

This gives a feeling like:

• Ah, that explains it.
• Now I see why it’s expensive.

So the sentence can carry a small sense of realization, not just simple cause-and-effect.

Yes. Both are good natural translations, depending on what nuance you want.

• That’s why it’s expensive.
  • straightforward explanation
• No wonder it’s expensive.
  • stronger feeling of realization or obviousness

Because of わけだ, the second one often captures the nuance especially well.

If you want to stay closer to the Japanese structure, you could also say:

• Since it’s an electric-assist bicycle, that explains why the price is high.

Japanese often expresses price with the adjective 高い:

• 値段が高い = the price is high
• naturally, this means it is expensive

English often prefers a verbal expression like costs a lot, but Japanese commonly uses the adjective.

Other examples:

• この店は高い。
  • This shop is expensive.
• この商品は値段が高い。
  • This product’s price is high.

So this is a very normal Japanese way to talk about something being expensive.

No. Normally, Japanese is written without spaces like this:

• 電動アシスト自転車だから、値段が高いわけだ。

Spaces are sometimes added in learning materials to make the parts easier to see, but native Japanese writing usually does not separate words this way.

So the standard written form is:

• 電動アシスト自転車だから、値段が高いわけだ。