An/The iPhone 12 costs too much.

[kadioguy]

(My original conversation)

Tom (from America): Will you buy an iPhone 12?

John (from Taiwan): No, an/the iPhone 12 costs too much in my country.

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a. An iPhone 12 costs too much in my country.

b. The iPhone 12 costs too much in my country.

In this context I think both can be used.

Sentence (a) means if I buy one (an iPhone 12), it will cost me a lot of money.

Sentence (b) means if I buy this cell phone ("iPhone 12" is an uncountable noun here), it will cost me a lot of money.

What do you think?

[jutfrank]

Use plural forms.

Tom: Do you think you'll buy an iPhone 12?
John. No, they/iPhone 12s cost too much in my country.

[Tarheel]

Kadioguy, if I say something costs too much it means I am not goiing to buy it.

[emsr2d2]

No native speaker would repeat the noun in the response.

John: Are you going to buy an iPhone 12?
Helen: No, they're too expensive.

Note that John's question is a closed question - it requires only a Yes/No answer. The responder doesn't have to elaborate unless they choose to.

[Tdol]

For me, a) is a single phone and b) is the phone considered as a model.