Na rynku była okazja: świeże kwiaty kosztowały mniej niż zwykle.

Na rynku means at the market / in the marketplace.

Here na is used with the locative case to show location, so rynek changes to rynku.

• dictionary form: rynek = market / town square
• location: na rynku = at the market

A useful contrast:

• na rynku = at the market
• na rynek = to the market

So if there were movement, Polish would use the accusative: Idę na rynek = I’m going to the market.

Polish does not have articles like a/an and the.

So na rynku can mean:

• at the market
• in the market square
• sometimes just at market

The exact meaning depends on context. This is very normal in Polish.

Because okazja is a feminine singular noun, and in the past tense Polish verbs agree with the subject in gender and number.

• okazja = feminine singular
• therefore: była = was (feminine singular)

Compare:

• był problem = there was a problem
• była okazja = there was a bargain/opportunity
• było pytanie = there was a question

So była matches okazja.

In this sentence, okazja most naturally means a bargain or a good deal.

The word can also mean opportunity in other contexts, but here the colon explains that the flowers were cheaper than usual, so the idea is:

• there was a bargain
• it was a good deal
• there was a special offer

So this is a case where the context tells you which English word fits best.

The colon introduces an explanation of what the okazja was.

So the structure is basically:

• There was a bargain: fresh flowers cost less than usual.

The second part explains the first part. This kind of punctuation works similarly in English.

Because świeże has to agree with kwiaty.

• singular: świeży kwiat = a fresh flower
• plural: świeże kwiaty = fresh flowers

Here kwiaty is plural and not masculine-personal, so the adjective takes the plural non-masculine-personal form świeże.

This agreement is very important in Polish: adjectives change to match the noun’s gender, number, and case.

Because the subject is świeże kwiaty, which is plural, and Polish past tense verbs agree with the subject.

• kwiaty = plural
• so the verb must also be plural: kosztowały = cost

More specifically, this is the non-masculine-personal plural ending.

Compare:

• Kwiaty kosztowały dużo. = The flowers cost a lot.
• Mężczyźni kosztowali... would be wrong in meaning here, but grammatically masculine-personal plural verbs usually end in -li, not -ły.

So -ły is exactly what you expect with kwiaty.

Both are possible, but they are slightly different in emphasis.

• kosztowały mniej niż zwykle = they cost less than usual
• były tańsze niż zwykle = they were cheaper than usual

The sentence with kosztowały mniej focuses directly on the price paid.
The version with tańsze focuses more on the flowers as cheaper items.

In this context, both sound natural.

Mniej means less, niż means than, and zwykle means usually / as usual.

So:

• mniej = less
• niż = than
• zwykle = usually

Together:

• mniej niż zwykle = less than usual

Here zwykle is an adverb, not an adjective. You can think of it as short for less than they usually cost.

A similar phrase is:

• więcej niż zwykle = more than usual

Yes. Zwykle and zazwyczaj are very close in meaning, and both can mean usually.

So you could also say:

• świeże kwiaty kosztowały mniej niż zazwyczaj

That would sound natural too. Zwykle is a little shorter and very common in everyday Polish.

The word order is natural, but Polish word order is more flexible than English word order.

This sentence:

• Na rynku była okazja: świeże kwiaty kosztowały mniej niż zwykle.

sounds neutral and smooth.

You could move things around for emphasis, for example:

• Była okazja na rynku...
• Świeże kwiaty na rynku kosztowały mniej niż zwykle.

These are possible, but they may shift the focus slightly. The original version sounds like a normal descriptive sentence, starting with the setting: at the market.

It can mean both, depending on context.

Rynek often means:

• marketplace
• town square
• in other contexts, even market in the economic sense

In this sentence, na rynku most likely suggests a real market or market square where flowers are being sold. So the idea is physical location, not the abstract economic market.

Yes. Both are reasonable.

Because Polish has no articles and because rynek can mean marketplace or town square, the exact English version depends on context.

The important grammar point is that na rynku gives the location, and the rest of the sentence explains what made it a bargain: fresh flowers cost less than usual.