Economical fallacies all over, there's a very simple way to measure the true cost of something, and provided government isn't subsidizing anything or skewing the market it actually measures things quite well. It's called a price. If you think that the quality of local produce is higher than the quality of non-local produce though, go ahead and buy things locally, it all comes down to what you're willing to spend for the produce and what quality you're demanding for your money. 
Here's two great articles on it by Art Carden: <a href="http://mises.org/daily/3026" rel="nofollow">http://mises.org/daily/3026</a>
<a href="http://mises.org/daily/3059" rel="nofollow">http://mises.org/daily/3059</a>