La kablo kostas unu dolaron.

La is the definite article, meaning the. So la kablo means the cable.

If you said just kablo, it would mean a cable or cable in a more general sense, depending on context. Esperanto has la for the, but it does not have a separate word for a/an.

In Esperanto, nouns normally end in -o. So kablo is a noun meaning cable.

This is one of the most basic and useful patterns in Esperanto:

• -o = noun
• -a = adjective
• -e = adverb
• -i = infinitive verb
• -as = present tense verb

So the -o tells you immediately that kablo is a noun.

Kostas means costs.

The ending -as marks the present tense in Esperanto. It is used for all subjects:

• mi kostas = I cost
• vi kostas = you cost
• ĝi kostas = it costs

Unlike English, the verb does not change depending on whether the subject is I, you, he, she, or it. The same present-tense ending -as is always used.

The -n ending marks the direct object.

In La kablo kostas unu dolaron, the thing being priced is one dollar. Esperanto treats the price as the direct object of kostas, so dolaro becomes dolaron.

This is very common in Esperanto:

• Ĝi kostas unu eŭron. = It costs one euro.
• La libro kostas kvin dolarojn. = The book costs five dollars.

So -n here is not random; it shows that one dollar is what the cable costs.

Because the amount is singular: one dollar.

• unu dolaron = one dollar
• du dolarojn = two dollars
• tri dolarojn = three dollars

The noun gets -j for plural and -n for direct object when needed. So:

• singular object: dolaron
• plural object: dolarojn

Since unu means one, the singular form is correct.

It actually can, depending on style and analysis.

Many speakers simply say unu dolaron, with the noun clearly marked as the object, and that is very normal and easy to understand.

You may also encounter unu dolaron as the standard practical form in learning materials. In more fully marked agreement, modifiers can also match the noun, so learners later see patterns where adjectives take the same endings as the nouns they modify.

The most important point for this sentence is that dolaron is the object form, and unu means one.

Because Esperanto usually says to cost something directly, without a preposition.

In English, we also say:

• It costs one dollar.

Esperanto works the same way here:

• Ĝi kostas unu dolaron.

So you do not need a word like for before the amount.

Yes, Esperanto word order is fairly flexible because endings show grammatical roles.

The most neutral order is:

• La kablo kostas unu dolaron.

But other orders are possible, especially for emphasis, such as:

• Unu dolaron kostas la kablo.

Because dolaron has -n, you can still tell it is the object. Even so, beginners should usually stick with the most normal order: subject + verb + object.

Grammatically, yes, but the meaning changes slightly.

• La kablo kostas unu dolaron. = The cable costs one dollar.
• Kablo kostas unu dolaron. = A cable costs one dollar or Cable costs one dollar, depending on context.

If you are talking about one specific cable, la is the natural choice.

It is a normal Esperanto word, though of course it comes from the international word dollar.

Esperanto often adapts international words to its own spelling and grammar:

• dollar → dolaro
• plural: dolaroj
• object form: dolaron
• plural object: dolarojn

So once borrowed, it behaves like any regular Esperanto noun.

A simple approximate pronunciation is:

lah KAH-bloh KOS-tahs OO-noo doh-LAH-ron

A few useful points:

• a is like the a in father
• o is like a pure o, not the English diphthong in go
• u is like oo in food
• stress is usually on the second-to-last syllable:
  • KA-blo
  • KOS-tas
  • do-LA-ron

Esperanto pronunciation is very regular, much more regular than English.

You would say:

La kablo kostas du dolarojn.

Here is what changed:

• du = two
• dolaro → dolaroj because it is plural
• dolaroj → dolarojn because it is also the direct object

So:

• unu dolaron = one dollar
• du dolarojn = two dollars

Because kostas expresses price, while estas just means is.

• La kablo estas unu dolaro would sound like The cable is one dollar, which is not the normal way to express price.
• La kablo kostas unu dolaron correctly means The cable costs one dollar.

So when talking about price, kosti is the right verb.