Золото дорого.

In Russian, the verb to be is normally left out in the present tense.

So:

• Золото дорого = Gold is expensive / valuable
• literally: Gold expensive

This is completely normal Russian.
If you were talking about the past or future, you would use forms of быть:

• Золото было дорогим = Gold was expensive
• Золото будет дорогим = Gold will be expensive

Золото is in the nominative case, because it is the subject of the sentence.

The basic dictionary form is:

• золото = gold

In this sentence, Russian is simply saying something about gold, so nominative is the expected case.

Because золото is a neuter noun, and the predicate form here agrees with that.

• золото is neuter
• the short-form predicate is дорого

Compare:

• Хлеб дорог = Bread is expensive (masculine)
• Машина дорога = The car is expensive (feminine)
• Золото дорого = Gold is expensive (neuter)
• Товары дороги = The goods are expensive (plural)

So дорогой is not the right form here.

In this sentence, it is best understood as a short-form adjective used predicatively.

That matters because beginners often recognize дорого as an adverb meaning expensively, for example:

• Это стоит дорого = This costs a lot / This is expensive

But in Золото дорого, it is not modifying a verb. It is describing the subject золото, so it functions like expensive in Gold is expensive.

In practical learner terms: treat дорого here as the form used to say that a neuter subject is expensive.

Because дорогое and дорого do different jobs.

• дорогое is the full adjective form
• дорого is the short form, often used in predicate position

Russian commonly prefers the short form in sentences like:

• Золото дорого
• Дом велик
• Она права

Very roughly:

• дорогое золото = expensive gold (adjective directly before the noun)
• Золото дорого = Gold is expensive (predicate statement)

So дорогое would usually be used with a noun, not as the main predicate in this simple sentence.

A strong clue is the ending -о.

Many Russian nouns ending in -о are neuter, including:

• золото = gold
• окно = window
• письмо = letter

Because золото is neuter, the predicate form is дорого.

Yes. Russian word order is more flexible than English.

Both of these are possible:

• Золото дорого
• Дорого золото

But they do not feel exactly the same.

• Золото дорого is the most neutral and straightforward.
• Дорого золото sounds more marked or expressive, as if emphasizing expensive.

For a learner, Золото дорого is the safest normal order.

Usually, yes: expensive or costly is the most natural meaning.

The adjective дорогой can also mean dear in the emotional sense:

• дорогой друг = dear friend

But in Золото дорого, the meaning is almost certainly about value or price, not affection.

The stress is:

• зо́лото доро́го

A simple pronunciation guide:

• зо́лото ≈ ZO-lə-tə
• доро́го ≈ də-RO-gə

A few useful notes:

• Unstressed о is reduced in pronunciation, so it often sounds closer to a or ə than a clear English o.
• The stress is important: зо́лото, доро́го.

Russian has no articles.

So золото can mean:

• gold
• the gold

depending on context.

In this sentence, the most natural interpretation is gold in general.

By itself, it most naturally sounds like a general statement about gold as a material:

• Gold is expensive

Russian often uses a bare noun like this for general truths or broad statements.

If the speaker meant a specific piece of gold, context would usually make that clear.

Yes, and that is very common.

Compare:

• Золото дорого = Gold is expensive
• Золото стоит дорого = Gold costs a lot / Gold is expensive

The version with стоит is a little more explicitly about price.
The shorter sentence Золото дорого is a simple descriptive statement.