I don't have a problem when someone asks me what I've paid for my car. Why should I try to make it a secret when everyone who's interested can look it up at KIA's website?
The same goes for other stuff - why shouldn't I tell what I've paid for my sweater, shoes, coffee maker or other items? In the most case the question isn't asked for mere curiosity, but because people want to get something like the sweater, shoes, coffeemaker or whatever else too and therefore want to know how much they would have to invest.
However, I don't like if someone wants to know how much I've paid for my horses. Prizes for horses depend on many factors - health, gaits, education, pedigree, sometimes even colour (in my opinion it's rather foolish, but a lot of people are totally mad for black horses or want at least black brown or dark brown. They don't even look at chestnuts and would never buy a gray).
"As long as the question is asked for information, I answer it. But when it's asked out of mere curiosity, I refuse an answer."