Learn Swedish: Tidningarna kostar tjugo kronor bunten. - The newspapers cost twenty kronor per bundle.

In Swedish, the most natural way to express unit pricing is to simply use the definite singular form of the unit. Here, bunten literally means 'the bundle', but it functions to mean 'per bundle' or 'a bundle'. No preposition is needed for physical units of measure or groupings.

Would it be wrong to say per bunt instead?

Not at all. You can absolutely say tjugo kronor per bunt, which uses the indefinite singular, and it means the exact same thing. However, using the definite form without a preposition is highly idiomatic and is what you will hear most often in Swedish markets and stores.

How do I know if bunt is an en-word or an ett-word from this sentence?

You can tell it is an en-word because the definite suffix used here is -en (bunten). If it were an ett-word, like kilo, you would see an -et ending instead, such as in the phrase tjugo kronor kilot (twenty kronor a kilo).

Can I use this exact same structure for rates of time, like saying it costs twenty kronor 'an hour'?

Not quite. While physical units and groupings (like a bundle, a kilo, or a piece) drop the preposition entirely, time expressions still require one. To say 'an hour' or 'a week', you must use a preposition alongside the definite noun, such as i timmen or i veckan.