Perayauan itu mahal, apatah lagi perayauan antarabangsa.

In this sentence, perayauan means roaming, especially mobile phone/network roaming.

It comes from the root rayau, which has the basic idea of wandering or roaming. In telecom usage, perayauan is the standard noun for roaming.

So:

• perayauan = roaming
• perayauan antarabangsa = international roaming

Itu often means that, but in sentences like this it can also mark something already known or under discussion.

So Perayauan itu mahal can mean something like:

• That roaming is expensive
• Roaming is expensive, with a slight sense of the roaming we’re talking about

Malay often uses itu and ini more flexibly than English uses that and this.

Malay usually does not need a verb like is/are between the subject and an adjective.

So:

• Perayauan itu mahal = Roaming is expensive
• literally more like That roaming expensive

This is completely normal in Malay.

Yes. Mahal means expensive, and it commonly works as the main predicate in a sentence.

Examples:

• Kereta itu mahal = That car is expensive
• Makanan di sini mahal = Food here is expensive

So in your sentence, mahal is the main comment about perayauan itu.

Apatah lagi is used to add something that is even more true, more extreme, or more obvious than what was just said.

In English, depending on context, it can be translated as:

• let alone
• much less
• all the more so
• especially

In this sentence:

• Perayauan itu mahal, apatah lagi perayauan antarabangsa means:
• Roaming is expensive, let alone international roaming.

The idea is: if ordinary roaming is expensive, then international roaming is even more so.

It links one statement to a stronger or more extreme follow-up.

Pattern:

• statement 1
• apatah lagi
  • something even more extreme

Here:

• Perayauan itu mahal = Roaming is expensive
• apatah lagi perayauan antarabangsa = let alone international roaming

The second part is somewhat elliptical: Malay does not need to repeat everything if it is already understood.

A fuller version could be understood as:

• Perayauan itu mahal, apatah lagi perayauan antarabangsa mahal but repeating mahal is unnecessary.

Because Malay often omits words that are obvious from context.

So:

• Perayauan itu mahal, apatah lagi perayauan antarabangsa naturally means:
• Roaming is expensive, let alone international roaming which is even more expensive

The adjective mahal is understood from the first clause.

This kind of omission is very common and natural.

In Malay, modifiers usually come after the noun.

So:

• perayauan antarabangsa = international roaming
• noun perayauan
  • modifier antarabangsa

This is the normal Malay word order, similar to:

• sekolah antarabangsa = international school
• penerbangan antarabangsa = international flight

Antarabangsa means international.

It is made from:

• antara = between
• bangsa = nation/people

So the literal sense is something like between nations, which developed into international.

Sometimes yes, but let alone or much less is often closer here.

Compare the feeling:

• especially international roaming sounds like one example being highlighted
• let alone international roaming clearly shows that international roaming is an even stronger case

So in this sentence, let alone international roaming is usually the best match.

It is generally neutral to somewhat formal. It sounds natural in writing, news, customer service, telecom contexts, or general explanation.

The word apatah lagi is perfectly common, but it can sound a bit more polished than very casual everyday speech.

In very casual speech, people might choose other phrasing, but this sentence is completely standard and natural.

Yes. Some possible alternatives are:

• Perayauan itu mahal, lebih-lebih lagi perayauan antarabangsa.
• Perayauan antarabangsa lebih mahal lagi.
• Perayauan memang mahal, terutamanya perayauan antarabangsa.

These are slightly different in nuance:

• apatah lagi = let alone / much less
• lebih-lebih lagi = even more so
• terutamanya = especially / particularly

Your original sentence is concise and elegant.