I'm not so sure but I think 'a car of $30,000' simply means that the car is worth of $30,000; and 'a car for $30,000' means that somebody exchange $30,000 for a car.
What is the difference in meaning between the phrase using 'of' and the other with 'for' do you think?
'A car of $30,000' is the phrase I made up. I'm learning about the preposition 'of' and pick up one of its usage 'used with measurements and expressions of time, age, etc.'. There are some examples for this case, like '2 kilos of potatoes, an increase of 2%, a girl of 12'. With that I think maybe the phrase 'a car of $30,000' matches the concept.
I got feedbacks from somes ell users, all of them are not with me about 'a car of $30,000'. The thing that keeps bother me is that preposition 'of' can be used to show possession, why can it not be applied in this case, 'a car of $30,000'?