Hún sagði að níutíu þúsund væri of há leiga fyrir svona litla íbúð.

Að here means that and introduces a subordinate clause: she said that ...

So the sentence breaks down like this:

• Hún sagði = she said
• að níutíu þúsund væri of há leiga ... = that ninety thousand was too high a rent ...

In Icelandic main clauses, the finite verb usually follows V2 word order, but subordinate clauses introduced by words like að do not follow that same pattern. That is why you get:

• að níutíu þúsund væri ...

and not a main-clause-style order.

Væri is the past subjunctive of vera (to be).

After verbs like sagði (said), Icelandic often uses the subjunctive in indirect or reported speech, especially when reporting someone's statement, opinion, or judgment rather than simply presenting it as a plain fact.

So:

• Hún sagði að ... væri ...

is a very natural way to say:

• She said that ... was ...

In English, we normally just use was, but Icelandic often shows this extra nuance with the subjunctive.

Yes. In Icelandic, of often means too in the sense of excessively.

So:

• of há leiga = too high a rent

This of is not related to the English preposition of. It is an adverb.

A few similar examples:

• of dýrt = too expensive
• of stór = too big
• of lítil = too small

Yes. That is very common.

When talking about money, Icelandic often leaves out krónur if the context makes it obvious. So níutíu þúsund here is naturally understood as:

• níutíu þúsund krónur = 90,000 krónur

English does the same kind of thing sometimes:

• It costs ninety thousand.

where the currency is understood from context.

Because the amount is being treated as one sum of money, not as many separate items.

So níutíu þúsund functions as a single amount, and singular agreement is natural:

• níutíu þúsund væri ... = ninety thousand was ...

English works similarly in sentences like:

• Ninety thousand is too much.

Even though the number is large, it is understood as one amount.

Because há agrees with leiga, not with níutíu þúsund.

• leiga = rent
• leiga is a feminine singular noun
• therefore the adjective must also be feminine singular: há

So:

• of há leiga = too high a rent

A useful way to see the structure is:

• níutíu þúsund = the subject
• væri of há leiga = was too high a rent

The adjective describes the noun leiga, so it matches leiga in gender, number, and case.

It is in the accusative, because fyrir takes the accusative in this meaning.

So:

• fyrir svona litla íbúð = for such a small apartment

Here is what is happening:

• íbúð is a feminine singular noun
• after fyrir, it is accusative
• the adjective litla matches it

One small detail: the noun íbúð looks the same in nominative and accusative singular, so the adjective helps make the case clearer.

Svona here means something like:

• such
• this kind of
• this sort of
• this small

So:

• svona litla íbúð can be understood as such a small apartment or an apartment this small

It is a very common everyday word in Icelandic and often adds a conversational sense of like this / like that / of this kind.

Here leiga means rent, specifically the amount of rent being charged.

So the idea is not the general act of renting, but rather:

• the rent level
• the rent amount

That is why of há leiga means:

• too high a rent
• rent that is too high

This is a very natural Icelandic way to express the idea.