Cold calling: What's the best response to this specific question?

[Steven McPherson]

I've been doing a lot of cold calling lately.  They are property owners that have little patience with me to start out with.  When I say I am interested in buying their house, their immediate response is "How much do you want to buy if for?"  I don't know anything about the house at this point, other than its vacant.

What is the best response to that question?  Do I give them an estimate or do I put the ball back in their court and ask how much they're willing to sell for?  Or is there a better response?  Thanks for the advice.