Το σπίτι κοστίζει ένα εκατομμύριο ευρώ.

Σπίτι is a neuter noun, so it takes the neuter definite article το.

• ο = masculine the
• η = feminine the
• το = neuter the

Many Greek nouns ending in -ι are neuter, and σπίτι is one of them.

Κοστίζει means costs.

It is the 3rd person singular present tense form of κοστίζω = to cost.

So:

• κοστίζω = I cost / to cost
• κοστίζει = it costs / he costs / she costs

In this sentence, it means it costs, referring to the house.

The ending -ει is a common ending for the 3rd person singular in the present tense in Modern Greek.

So if the subject is he, she, it, Greek often uses a form like this:

• κοστίζω = I cost
• κοστίζεις = you cost
• κοστίζει = he/she/it costs

Since το σπίτι is singular, κοστίζει is the correct form.

Because εκατομμύριο is also neuter.

The word ένα is the neuter form of one:

• ένας = one (masculine)
• μία / μια = one (feminine)
• ένα = one (neuter)

So Greek says ένα εκατομμύριο because εκατομμύριο is a neuter noun.

Yes. In Greek, εκατομμύριο behaves like a noun meaning million.

That is why it works a bit like this:

• ένα εκατομμύριο ευρώ = one million euros
• δύο εκατομμύρια ευρώ = two million euros

So the number agrees with εκατομμύριο / εκατομμύρια, and ευρώ comes after it to show what is being counted.

Because ευρώ stays the same in modern usage for both singular and plural.

So you get:

• ένα ευρώ = one euro
• δύο ευρώ = two euros
• ένα εκατομμύριο ευρώ = one million euros

Unlike English, where euro becomes euros, Greek normally keeps ευρώ unchanged.

After numbers, Greek normally does not use the definite article with the thing being counted.

So you say:

• δέκα ευρώ = ten euros
• χίλια ευρώ = a thousand euros
• ένα εκατομμύριο ευρώ = one million euros

You would not normally say ένα εκατομμύριο τα ευρώ here.

Το σπίτι is the subject, so it is in the nominative.

The price expression ένα εκατομμύριο ευρώ functions as the amount that the house costs, and this kind of expression is treated like an object/amount phrase, so it is effectively in the accusative.

In this particular sentence, the forms do not visibly change much because:

• σπίτι is neuter, and neuter nominative and accusative often look the same
• εκατομμύριο is also neuter, so nominative and accusative singular are the same
• ευρώ does not change here

So even though the grammar matters, the forms are easy to recognize because they look unchanged.

Yes, Greek word order is more flexible than English, but the neutral, most natural order here is:

Το σπίτι κοστίζει ένα εκατομμύριο ευρώ.

That is basically:

subject + verb + amount

You can change the order for emphasis, but then the sentence may sound more marked or dramatic. For example, putting the amount first would emphasize the price more strongly.

A rough pronunciation is:

toh SPEE-tee ko-STEE-zee EH-na eh-ka-toh-MEE-ree-oh ev-ROH

A few helpful points:

• σπίτι = SPEE-tee
• κοστίζει = ko-STEE-zee
• ευρώ sounds like ev-ROH, because ευ is pronounced ev before a voiced sound like ρ

The stress marks in Greek show you where the emphasis goes:

• σπίτι
• κοστίζει
• ένα
• εκατομμύριο
• ευρώ

Yes. Another common verb is στοιχίζω.

So you may also hear:

Το σπίτι στοιχίζει ένα εκατομμύριο ευρώ.

Both are possible. Κοστίζω is very straightforward and common, especially for stating a price plainly. Στοιχίζω is also common and natural.

You would make the subject plural and change the verb to plural too:

Τα σπίτια κοστίζουν ένα εκατομμύριο ευρώ.

Changes:

• το σπίτι → τα σπίτια = the houses
• κοστίζει → κοστίζουν = cost

The amount ένα εκατομμύριο ευρώ stays the same.