Είναι από τη μία κοντά, από την άλλη ακριβό.

It means on the one hand ..., on the other hand ....

Literally, it is something like from the one side ..., from the other side .... In Greek, this is a very common way to present two contrasting points about the same thing.

So in:

Είναι από τη μία κοντά, από την άλλη ακριβό.

the speaker is weighing two sides of the situation:

• a positive side: it’s close
• a negative side: it’s expensive

This is due to a very common pronunciation/spelling pattern in Greek.

The full feminine accusative singular article is την. But before many consonants, especially in everyday usage, the final -ν is often dropped:

• την μία → τη μία
• but την άλλη stays την άλλη because άλλη starts with a vowel

So:

• από τη μία
• από την άλλη

Both are normal and idiomatic here.

They are in the accusative feminine singular.

That is because they come after the preposition από, which normally takes the accusative in Modern Greek.

So:

• από τη μία
• από την άλλη

Both parts are built the same way:

• από
  • article + feminine word in the accusative

In this expression, Greek is really implying something like:

• από τη μία πλευρά
• από την άλλη πλευρά

or

• από τη μία μεριά
• από την άλλη μεριά

Both πλευρά and μεριά are feminine nouns, so the words μία and άλλη are feminine too.

In everyday Greek, the noun is usually left out because the expression is fixed and everyone understands it.

Here κοντά is being used as an adverb, meaning near, close by, or not far away.

So:

• Είναι κοντά = It is close / nearby

This is different from using an adjective such as:

• κοντινό μαγαζί = a nearby shop
• κοντινή στάση = a nearby stop

In your sentence, the speaker is describing location in a general way, so the adverb κοντά is the natural choice.

Because it agrees with the thing being talked about, which is understood from context.

Greek often leaves out the subject when it is obvious. So Είναι ... ακριβό means It is expensive, where it refers to something unstated but understood.

If that thing is neuter, then the adjective is neuter too:

• το σπίτι → είναι ακριβό
• το διαμέρισμα → είναι ακριβό

If the noun were feminine or masculine, the adjective would change:

• η περιοχή είναι ακριβή
• ο καφές είναι ακριβός

So ακριβό tells you the implied noun is probably neuter singular.

Greek often omits subject pronouns when they are understood from context.

So:

• Είναι ακριβό literally has no separate word for it
• but in natural English, we translate it as It is expensive

This is extremely common in Greek:

• Είναι καλό. = It is good.
• Δεν είναι εύκολο. = It isn’t easy.

The verb ending and the situation usually make the subject clear enough.

Yes, but in many cases the difference is small.

• μια is the common everyday unstressed form
• μία is the more clearly stressed form

Both can mean a/an or one, depending on context.

In expressions like από τη μία, από την άλλη, the spelling μία is very common because the contrast is a bit more emphatic, almost like the one side ... the other side.

In everyday speech, learners may hear something that sounds very close to μια anyway.

The sentence is complete as it stands.

Greek often leaves out information that is obvious from context. So a fuller version might be something like:

• Το σπίτι είναι από τη μία κοντά, από την άλλη ακριβό.
• Το ξενοδοχείο είναι από τη μία κοντά, από την άλλη ακριβό.

But once the topic is known, Greek does not need to repeat the noun.

So the short sentence sounds natural and idiomatic.

Yes, Greek word order is fairly flexible, though some versions sound more natural than others.

Your sentence:

Είναι από τη μία κοντά, από την άλλη ακριβό.

is natural and clear.

You could also say:

• Από τη μία είναι κοντά, από την άλλη είναι ακριβό.
• Από τη μία κοντά, από την άλλη ακριβό.
  (more elliptical, especially in conversation)

Repeating είναι can make the structure feel slightly more explicit, but leaving it out in the second half is very common.

The comma separates the two contrasting parts of the sentence.

So the structure is:

• από τη μία κοντά
• από την άλλη ακριβό

This mirrors the pause you would make in speech, just like in English:

• On the one hand, it’s close; on the other hand, it’s expensive.

The comma helps show that the speaker is balancing two opposite considerations.