buhindai ga takai desu.

部品代 means the cost of parts or parts fee.

It is made up of:

• 部品 = parts, components
• 代 = charge, cost, fee

So this sentence is specifically talking about the price of the parts themselves, not necessarily the total price of a repair or service.

For example:

• 部品代 = parts cost
• 修理代 = repair fee
• 送料 = shipping cost

In this sentence, が marks 部品代 as the thing being described.

So:

• 部品代 が 高いです。
• literally: As for the parts cost, it is high / expensive.

A very natural English translation is The parts are expensive or The cost of the parts is high.

In simple terms, が is marking what has the property 高い.

Yes. 部品代は高いです is also natural.

The difference is mainly one of focus and context:

• 部品代が高いです
  can sound like the parts cost is what is high
• 部品代は高いです
  sounds more like as for the parts cost, it is high

Very roughly:

• が often highlights or identifies
• は often introduces a topic or contrast

For example, if you are comparing costs:

• 工賃は安いですが、部品代は高いです。
  The labor is cheap, but the parts are expensive.

So in isolation, both are possible, but は is often very common when talking about a topic generally.

Because Japanese adjectives can act like predicates by themselves.

In English, you need something like:

• The parts cost is high
• The parts are expensive

But in Japanese, 高い already functions as is high / is expensive.

So:

• 部品代が高い。 = The parts cost is high.

The です at the end does not work exactly like the English verb to be. Here it mainly makes the sentence polite.

Because です makes the sentence polite.

• 部品代が高い。 = plain / casual
• 部品代が高いです。 = polite

This is a very common pattern with い-adjectives:

• 安いです = is cheap
• 高いです = is expensive / high
• 難しいです = is difficult

So 高いです is a normal polite form.

Yes, 高いです is absolutely normal and correct in modern Japanese.

What learners usually hear is that い-adjectives do not need です to form a sentence, and that is true:

• 高い。 = complete sentence

But you can still add です for politeness:

• 高いです。

So the important point is:

• 高い already carries the meaning
• です adds politeness, not the core adjective meaning

Here it means expensive.

高い can mean both:

• high for height, level, etc.
• expensive for prices and costs

Because the subject is 部品代 (cost of parts), the natural meaning is expensive or high in price.

So these English translations are both fine:

• The parts are expensive.
• The cost of the parts is high.

The structure is:

• noun + が + adjective + です

In this case:

• 部品代 = noun
• が = subject marker
• 高い = adjective
• です = politeness

So the pattern is:

• X が 高いです
• X is expensive / high

Other examples:

• この店の料理が高いです。
  The food at this restaurant is expensive.
• 家賃が高いです。
  The rent is high.

Yes, it is read ぶひんだい.

Breakdown:

• 部品 = ぶひん
• 代 = だい

So:

• 部品代 = ぶひんだい

Yes, it is understandable and natural.

That said, in real conversation, you may also hear:

• 部品代は高いです。
• 部品代が高いですね。
• 部品代、高いです。

These all sound natural, with slightly different nuance.

For example:

• ですね adds a softer, conversational tone
• は may sound more topical or contrastive
• dropping particles in speech can happen in casual conversation

But 部品代が高いです。 is perfectly fine Japanese.

Yes. If you want a plain, less polite style, you can say:

• 部品代が高い。

This is natural in casual speech, informal writing, inner thoughts, or dictionary-style examples.

Compare:

• 部品代が高いです。 = polite
• 部品代が高い。 = plain / casual

So the sentence without です is still complete.

It usually means the amount charged for the parts.

That is an important nuance. 部品代 is not just parts as physical objects. It is the cost/charge for the parts.

So if you are at a repair shop, this could mean something like:

• The parts charge is expensive.
• The replacement parts cost a lot.

If you wanted to talk about the parts themselves more directly, you might use 部品 instead of 部品代, but then the nuance would be a little different.

No, standard Japanese normally does not use spaces between words.

It would usually be written as:

• 部品代が高いです。

Spaces are often added in learning materials to make the structure easier to see:

• 部品代　が　高い　です。

So the spaced version is just a teaching aid, not normal everyday writing.