Translation:I would buy this car if it were cheaper.
I think that "were" can be used for all persons in conditionals so my translation as "I would buy this car if it were cheaper" should be correct
That would be correct, I would say, although the "were" is a subjunctive in English, something we rarely think about.
I think, I would prefer "if it would be" to be correct as well.
It would make translating into English a bit more non-native speaker friendly.
"If it would be" is not grammatically correct, although I think it is used colloquially in some places.
As had been stated, if you're going to teach people the subjunctive in one language, you should probably be using it correctly in the primary language.