yuèzūfèi hé ānzhuāngfèi dōu bù guì.

Because 贵 is an adjective, and in Mandarin adjectives can act as the predicate by themselves.

So:

• 贵 = expensive
• 不贵 = not expensive

You do not normally say 是贵 here.

Compare:

• 这个很贵。 = This is expensive.
• 这个不贵。 = This is not expensive.

Using 是 would sound unnatural in this kind of sentence.

都 means both or all, depending on how many things you are talking about.

In this sentence, there are two things:

• 月租费
• 安装费

So 都不贵 means both are not expensive.

A very common pattern is:

A 和 B 都 + predicate

So here:

• 月租费和安装费都不贵。
• The monthly fee and the installation fee are both not expensive.

都 usually comes after the full subject and before the comment/predicate about that subject.

So the structure is:

• 月租费和安装费 = the two things being discussed
• 都不贵 = the statement that applies to both of them

That is why the word order is:

月租费 和 安装费 都 不贵

not something like:

• 都月租费和安装费不贵 ❌

A useful rule is:

[things/persons mentioned] + 都 + [what is true about them]

Yes, in this sentence 和 works like and to connect two nouns:

• 月租费和安装费 = the monthly fee and the installation fee

It is a very common conjunction for linking nouns.

Other words can sometimes also mean and, such as:

• 跟
• 同
• 以及 (more formal)

But 和 is the most neutral and common choice here.

They are similar, but not exactly the same.

• 不贵 = not expensive
• 很便宜 = very cheap/inexpensive

不贵 is a bit softer and more neutral. It means the price is reasonable, but it does not necessarily mean it is extremely cheap.

For example:

• 这个不贵。 = This isn’t expensive.
• 这个很便宜。 = This is very cheap.

So 不贵 is often a more natural choice when someone simply wants to say the price is acceptable.

In Mandarin, when an adjective is used as the main predicate in an affirmative sentence, it often needs a degree word such as 很:

• 这个很贵。 = This is expensive.

But when the adjective is negated with 不, you usually do not need 很:

• 这个不贵。 = This is not expensive.

So:

• 贵 by itself can sound abrupt in many contexts
• 很贵 is the normal affirmative form
• 不贵 is the normal negative form

That is why 都不贵 sounds natural.

Both words end with 费, which means fee or cost.

月租费

• 月 = month
• 租 = rent
• 费 = fee/cost

So 月租费 is the monthly rental fee or monthly subscription fee, depending on context.

安装费

• 安装 = install / installation
• 费 = fee/cost

So 安装费 means installation fee.

This pattern is very common in Chinese:

• 学费 = tuition fee
• 服务费 = service fee
• 停车费 = parking fee

Even though 不 is normally fourth tone (bù), it changes to second tone when it comes before another fourth-tone syllable.

Since 贵 is fourth tone (guì), 不贵 is pronounced:

• bú guì

This is a very common tone change rule.

Examples:

• 不是 → bú shì
• 不对 → bú duì
• 不贵 → bú guì

So in actual speech, you should say bú guì.

Yes. In English, when there are exactly two things, both is usually the most natural translation.

So:

• 月租费和安装费都不贵。

can be understood as:

• Both the monthly fee and the installation fee are not expensive.

Mandarin still uses 都 even when there are only two items. It does not need a separate word that means only both.

Not in the same way.

• 都 means the statement applies to all the items mentioned.
• 也 means also.

So in this sentence, 都 is the correct word because you are saying one fact applies to both fees.

Correct:

• 月租费和安装费都不贵。

With 也, you would need a different structure:

• 月租费不贵，安装费也不贵。 = The monthly fee is not expensive, and the installation fee is also not expensive.

So 都 is more compact and natural for this sentence.