Transport kosztuje mniej.

Kosztuje is the 3rd person singular form of kosztować (to cost).

That form is used because transport is treated as a singular noun:

• transport kosztuje = transport costs

If the subject were plural, the verb would change:

• Transporty kosztują więcej. = The transports cost more.

The dictionary form is kosztować, which means to cost.

A few useful present-tense forms are:

• ja kosztuję = I cost
• ty kosztujesz = you cost
• on / ona / ono kosztuje = he / she / it costs
• my kosztujemy = we cost
• wy kosztujecie = you (plural) cost
• oni / one kosztują = they cost

In this sentence, we use kosztuje because transport is singular.

Mniej means less.

So kosztuje mniej literally means costs less.

Very often, Polish leaves out the comparison if it is already understood from context. So this can mean:

• less than before
• less than something else
• simply cheaper, in a general comparison

Because Polish, like English, often omits that part when it is obvious from context.

Compare:

• Transport kosztuje mniej. = Transport costs less.
• Transport kosztuje mniej niż dawniej. = Transport costs less than before.
• Transport kosztuje mniej niż samochód. = Transport costs less than a car.

So the shorter sentence is completely natural if the comparison is already understood.

Yes. Transport jest tańszy means Transport is cheaper.

Both are natural, but there is a slight difference in focus:

• Transport kosztuje mniej = focuses on the amount of money paid
• Transport jest tańszy = uses the adjective tańszy (cheaper) to describe transport

In many situations, they are very close in meaning.

This is the most neutral word order: subject + verb + adverb.

• Transport = subject
• kosztuje = verb
• mniej = adverb

Polish word order is more flexible than English, so other orders are possible for emphasis, for example:

• Mniej kosztuje transport
• Kosztuje mniej transport

But these sound marked or context-dependent. For a basic statement, Transport kosztuje mniej is the safest and most natural choice.

It is in the nominative case because it is the subject of the sentence.

The sentence structure is:

• Transport — nominative subject
• kosztuje — verb
• mniej — adverb

No object is needed here, so there is no extra noun in another case.

Yes. Transport is masculine inanimate.

That matters for agreement in other sentences, for example:

• Ten transport jest tani. = This transport is cheap.

Here:

• ten is the masculine demonstrative
• tani is the masculine adjective form

In Transport kosztuje mniej, the gender does not visibly affect kosztuje, because the present-tense verb form is the same for all singular genders in the 3rd person.

A rough English-friendly guide is:

TRAN-sport kosh-TOO-ye myeny

A few details:

• rz in kosztuje is not present here; the tricky part is sz, which sounds like English sh
• je in mniej sounds like ye
• mniej is pronounced roughly like myeny, but as one smooth syllable group rather than two clearly separate English words

A more Polish-style approximation would be:

• transport kosh-TOO-ye mnyey

No. In this sentence, mniej functions as an adverb because it modifies the verb kosztuje.

It tells us how it costs: less.

Compare:

• mniej kosztuje = costs less
• tańszy transport = cheaper transport

In the second example, tańszy is an adjective modifying the noun transport. In your sentence, mniej modifies the verb instead.