Etableringsgebyret og månedsleien er høye.

Those endings mark the definite form in Norwegian, often corresponding to English the.

• gebyret = the fee
• månedsleien = the monthly rent

So instead of usually putting a separate word before the noun, Norwegian often attaches definiteness to the end of the noun itself.

In this sentence:

• etableringsgebyret = the setup/establishment fee
• månedsleien = the monthly rent

Because the subject is plural in meaning: it refers to two things joined by og (and).

Norwegian predicate adjectives agree like this:

• høy for singular common-gender nouns
• høyt for singular neuter nouns
• høye for plural

Compare:

• Leien er høy. = The rent is high.
• Gebyret er høyt. = The fee is high.
• Gebyret og leien er høye. = The fee and the rent are high.

Even though each noun is singular by itself, together they form a plural subject, so høye is correct.

Er is the present tense of å være (to be).

So:

• er = is / are

In this sentence, the subject is plural in meaning, but Norwegian still uses er for both singular and plural in the present tense:

• Hun er = she is
• De er = they are

So Etableringsgebyret og månedsleien er høye uses er because it is simply the present tense form of to be.

Yes. Norwegian usually writes compound nouns as one word.

So:

• etablering
  • gebyr = etableringsgebyr
• definite form: etableringsgebyret

This is very normal in Norwegian. English often uses two words where Norwegian uses one compound word.

A good habit for learners is: if English has something like setup fee, monthly rent, train station, winter coat, Norwegian will very often write it as a single word.

The base compound is månedsleie:

• måned = month
• leie = rent
• månedsleie = monthly rent

That -s- is a very common linking element in Norwegian compounds. It does not usually mean possession here in the same way as English 's. It is just part of how many compounds are formed.

Then the definite ending is added:

• månedsleie → månedsleien

So the structure is:

• måned
  • s
    • leie
      • n

Because the sentence is talking about specific charges, not fees and rent in general.

So this is the difference:

• et etableringsgebyr og en månedsleie = a setup fee and a monthly rent
• etableringsgebyret og månedsleien = the setup fee and the monthly rent

When two specific things are being mentioned together, Norwegian normally marks each noun as definite.

Here it means high in price/cost, so in natural English it often corresponds to expensive.

With money-related words like these, høy / høyt / høye often means:

• high
• costly
• expensive

So for fees, prices, rent, taxes, and similar things, høye is very natural.

This is the normal word order for a simple statement in Norwegian:

• subject + verb + complement

So here:

• Etableringsgebyret og månedsleien = subject
• er = verb
• høye = complement/adjective

Norwegian is also a V2 language, which means the finite verb usually comes in the second position in main clauses. In this sentence, the subject comes first, so er comes second.

Not in the same way.

In your sentence, høye is a predicate adjective because it comes after er:

• ... er høye = are high

If you put the adjective before the nouns, Norwegian uses a different structure with double definiteness:

• det høye etableringsgebyret og den høye månedsleien

So:

• Etableringsgebyret og månedsleien er høye. = The setup fee and the monthly rent are high.
• det høye etableringsgebyret og den høye månedsleien = the high setup fee and the high monthly rent

Then the adjective would change to match that single noun.

For example:

• Etableringsgebyret er høyt.
  Here gebyr is a neuter noun, so the predicate adjective is høyt.

• Månedsleien er høy.
  Here månedsleien takes høy in the singular.

But when both are together:

• Etableringsgebyret og månedsleien er høye.

So this sentence is a very useful example of adjective agreement in Norwegian.