Nevím, jestli budu smlouvat o ceně, nebo auto koupím.

This is a very common Czech grammar question. The difference is aspect.

• smlouvat is imperfective
• koupit is perfective

In Czech:

• the future of an imperfective verb is usually made with budu + infinitive
  • budu smlouvat = I will be bargaining / I will bargain
• a perfective verb usually forms its future with what looks like the present tense
  • koupím = I will buy

So:

• budu smlouvat = future of an imperfective verb
• koupím = future of a perfective verb

You would normally not say budu koupit.

Here jestli means whether / if.

In this sentence, it introduces an indirect question after Nevím:

• Nevím, jestli... = I don’t know whether...

So the structure is:

• Nevím = I don’t know
• jestli budu smlouvat o ceně, nebo auto koupím = whether I’ll haggle over the price or buy the car

A more formal alternative is zda, but jestli is very common in everyday Czech.

Because Czech punctuation normally separates clauses more clearly than English.

• Nevím, jestli budu smlouvat o ceně...
  • the comma comes before the subordinate clause introduced by jestli
• ..., nebo auto koupím
  • here nebo joins two finite clauses, so a comma is used

The clauses are:

1. Nevím
2. jestli budu smlouvat o ceně
3. nebo auto koupím

So the commas are standard and expected.

Smlouvat means to haggle, to bargain, or to negotiate in the sense of trying to get a better deal.

• o ceně literally means about the price
• together, smlouvat o ceně means to haggle over the price or to negotiate the price

So this is a natural phrase when talking about buying something, especially something expensive like a car.

Ceně is in the locative singular.

That is because the verb smlouvat is used here with the preposition o, and o in this meaning takes the locative:

• o ceně = about / over the price

The noun is:

• cena = price
• locative singular: ceně

This is something you often have to learn together with the verb:

• mluvit o něčem = talk about something
• smlouvat o něčem = bargain over something

Auto is a neuter noun, and in the singular its nominative and accusative forms are the same.

Here it is the direct object of koupím:

• auto koupím = I will buy the car

Forms:

• nominative: auto
• accusative: auto

So the case does change in function, but the form happens to stay the same.

Yes, both are possible.

Czech word order is more flexible than English, and it often changes according to emphasis or information structure.

Your original sentence:

• Nevím, jestli budu smlouvat o ceně, nebo auto koupím.

Possible alternative:

• Nevím, jestli budu o ceně smlouvat, nebo koupím auto.

Both are understandable and natural. The difference is mostly one of emphasis and rhythm, not basic meaning.

The original version slightly highlights:

• smlouvat o ceně
• auto koupím

The alternative sounds a bit more neutral to some speakers.

Yes. Here nebo means or and connects two alternatives:

• budu smlouvat o ceně
• auto koupím

So the speaker does not know which of the two they will do.

Czech also has:

• anebo = a slightly fuller form of nebo
• či = a more formal/literary or

But nebo is the normal everyday choice.

Czech often places the most important or informative element later in the clause. In auto koupím, the object auto comes before the verb, which is perfectly possible in Czech.

So:

• nebo auto koupím literally looks like
• or the car I’ll buy

This does not sound as marked in Czech as it would in English.

You could also say:

• nebo koupím auto

That would also be correct. The version with auto koupím may place a bit more focus on auto.

In normal interpretation, yes: it presents two alternatives.

• budu smlouvat o ceně = I’ll haggle over the price
• nebo auto koupím = or I’ll buy the car

So the meaning is roughly:

• I don’t know whether I’ll try to negotiate the price, or just buy the car.

In real life, of course, someone might haggle and then buy. But this sentence presents them as two competing options in the speaker’s mind.

Yes, in English we often say:

• I don’t know if...
• I don’t know whether...

Both are natural translations.

But grammatically, in this Czech sentence, jestli is introducing an indirect yes/no question, so whether is often the clearest explanation for learners.

So:

• Nevím, jestli... = I don’t know whether... or more naturally in everyday English:
• I don’t know if...