Det är en konstig kostnad.

In this sentence, det means it/that.

Swedish often uses det är ... in the same way English uses it is ... or that is ...:

• Det är bra. = It is good.
• Det är en konstig kostnad. = That/it is a strange cost/expense.

So det is the subject of the sentence.

Because kostnad is an en-word in Swedish.

Swedish nouns have two grammatical genders:

• en-words
• ett-words

Since kostnad is en kostnad, both the article and the adjective must match that:

• en konstig kostnad ✔
• ett konstigt kostnad ✘

So the pattern is:

• en + adjective in common gender + noun
• ett + adjective in neuter form + noun

Adjectives in Swedish change form depending on the noun.

Here, kostnad is an en-word, so the adjective takes the en-word/common gender form:

• en konstig kostnad

Compare:

• ett konstigt problem = a strange problem

So:

• konstig is used with en-words
• konstigt is used with ett-words

Kostnad usually means cost or expense.

It often refers to:

• an amount of money something costs
• an expense in a business or financial context

Examples:

• höga kostnader = high costs/expenses
• en oväntad kostnad = an unexpected expense

It is not always the same as price.
For price, Swedish often uses pris.

A rough comparison:

• pris = the listed or selling price
• kostnad = the cost/expense

This is a very standard Swedish sentence pattern:

• Subject + verb + complement

So here:

• Det = subject
• är = verb
• en konstig kostnad = complement

This is directly similar to English:

• It is a strange cost.

Swedish main clauses normally put the finite verb in the second position, and this sentence follows that rule naturally.

Because the phrase is indefinite singular: a strange cost/expense.

In Swedish:

• en kostnad = a cost/an expense
• kostnaden = the cost/the expense

So:

• en konstig kostnad = a strange cost
• den konstiga kostnaden = the strange cost

The article en works like English a/an here.

A careful learner-friendly pronunciation might be approximated as:

deh air en KON-stig KOST-nad

A few notes:

• det is often pronounced more like de in everyday speech
• är sounds a bit like air
• konstig has stress on the first syllable: KON-stig
• kostnad has stress on the first syllable: KOST-nad

In natural speech, the sentence may sound smoother and less fully pronounced than it looks in writing.

Yes, depending on context, English might translate det as either it or that.

For example:

• if you are pointing something out, English might say That is a strange cost
• if you are already talking about it, English might say It is a strange cost

Swedish still commonly uses det in both cases.

Yes. Konstig means strange, but depending on context, other adjectives may sound more natural.

For example:

• Det är en märklig kostnad. = That is an odd/remarkable expense.
• Det är en ovanlig kostnad. = That is an unusual expense.
• Det är en orimlig kostnad. = That is an unreasonable cost.

So konstig is correct, but the best adjective depends on what kind of strange you mean.

The plural is:

• en kostnad = a cost
• kostnader = costs/expenses

So in plural, the sentence could become:

• Det är konstiga kostnader. = Those are strange costs.

Notice two things:

• the noun becomes kostnader
• the adjective becomes konstiga in plural

So Swedish adjective forms often work like this:

• en konstig kostnad
• ett konstigt problem
• konstiga kostnader