Við borgum áttatíu þúsund í leigu og tuttugu þúsund fyrir hita á mánuði.

Borgum is the 1st person plural present tense of að borga (to pay).

So:

• ég borga = I pay
• við borgum = we pay

The ending -um is a very common present-tense ending for we in Icelandic verbs.

Við means we. Icelandic often keeps the subject pronoun, especially in normal everyday statements, so Við borgum is the standard way to say we pay.

Sometimes pronouns can be omitted in limited contexts, especially if the subject is already very clear, but for learners it is best to think of Við borgum as the normal full form.

Because the same verb applies to both amounts, Icelandic does not need to repeat it.

So the structure is:

• Við borgum áttatíu þúsund í leigu
• og tuttugu þúsund fyrir hita

That is exactly like English We pay 80,000 in rent and 20,000 for heating. The second part is understood as continuing the same verb: we pay.

This is mostly a matter of idiomatic usage.

In Icelandic, when talking about an amount paid as rent, it is very common to say:

• borga X í leigu = pay X in rent

But for services or things you are paying for, Icelandic often uses:

• borga X fyrir hita = pay X for heating
• borga X fyrir rafmagn = pay X for electricity

So English learners should treat these as common patterns:

• í leigu
• fyrir hita

They are not interchangeable in the most natural everyday usage.

Leigu is the oblique form of leiga, which means rent.

The dictionary form is:

• leiga = rent

After a preposition, Icelandic nouns usually appear in a non-nominative case, so you get leigu rather than leiga.

A useful thing for learners to remember is simply the whole phrase:

• í leigu = in rent / as rent

The dictionary form is:

• hiti = heat

After fyrir, Icelandic normally uses the accusative case, so hiti becomes hita.

So:

• hiti = heat
• fyrir hita = for heating / for heat

This is a very common pattern in Icelandic: prepositions often control a specific case.

Yes. In this kind of sentence, fyrir hita means paying for heating or heat service, not just heat in an abstract sense.

So it refers to a household expense, like:

• heating
• hot water / heating costs, depending on context
• the heating part of utilities

This is very natural Icelandic usage.

Á mánuði means per month or a month in the sense of a monthly rate.

So the sentence means that these are the amounts paid each month.

This is a very common Icelandic time-expression pattern:

• á dag = per day
• á viku = per week
• á mánuði = per month
• á ári = per year

Even if the literal preposition is á, it is best to learn the whole phrase as an expression meaning per.

Icelandic often leaves out the currency name when it is obvious from context.

So:

• áttatíu þúsund = eighty thousand
• tuttugu þúsund = twenty thousand

In real life, this usually means krónur if the context is Icelandic money, but speakers often do not say krónur every time.

English does this too in some situations, like Rent is 2,000 a month where dollars/pounds/euros may be understood from context.

The numbers are:

• tuttugu = twenty
• áttatíu = eighty
• þúsund = thousand

So:

• áttatíu þúsund = 80,000
• tuttugu þúsund = 20,000

A useful point is that Icelandic number expressions often work very similarly to English in this kind of phrase: eighty thousand, twenty thousand, and so on.

Yes, this word order is completely natural.

The sentence first gives the two expenses and then adds the time frame at the end:

• Við borgum ... á mánuði.

That works like English We pay ... per month.

You can sometimes move time expressions around in Icelandic for emphasis, but the version here is very standard and natural.

It gives two separate monthly costs:

• áttatíu þúsund í leigu = 80,000 in rent
• tuttugu þúsund fyrir hita = 20,000 for heating

Then á mánuði applies to the whole statement, meaning both of those are paid each month.

It would sound less natural in this context. Icelandic strongly prefers the idiomatic phrase:

• borga X í leigu

So even though English uses for rent in some phrases, Icelandic usually does not match that preposition here. This is one of those places where it is better to memorize the whole expression rather than translate word-for-word from English.