HELEN'S ANSWER: It is pretty tacky to ask a person how much something they have costs. I still like the answer a friend told me to use years ago. When asked a question that you don't want to answer, you could say ”Why do you ask?” It slows the person down and makes them rethink the question. They might say “oh, I wanted to get myself one,” or “I just wanted to know,” but it does shed light on the fact that it might bother you to tell them.
You are certainly not obligated to answer how much or where it came from. However, I usually answer both questions honestly as I am flattered if anyone likes what I have.
GUEST'S ANSWER: Conner Rohwer, intern for The Oklahoman this summer: If that is his standard answer, it may be more of a habit than his curiousity. Obviously, you don't want to seem rude, but you don't have to share the information with him if you are not comfortable doing so. A simple “as much as I was willing to spend” or “too much” are completely acceptable without really giving away how much you spent. But then again, if you got a good deal on something, why not brag about it?