1 Corinthians 10:28

But if any man say unto you, this is offered in sacrifice unto idols, eat not for his sake that shewed it, and for conscience sake: for the earth is the Lord's, and the fulness thereof (KJV)

Then: In discussing these verses Fee (p. 490) keeps coming back to Paul's major reason. What Paul does is always for the sake of another's salvation. He will not eat if eating interferes with that goal; otherwise, he sees no problem with the eating. One might even speculate that due to economic necessity of purchasing lower-priced goods and allowing more to be available for the work of the church or the benefit of an individual in low economic circumstances, purchasing idol meat is just "expedient."

Now: Not much can be added to translate into today's world. Consider the salvation of others and do what's economically sensible as long as it doesn't impede the work of Christ. The principle applies just as much as today.

Extra source: The First Epistle to the Corinthians by Gordon D. Fee (Eerdman's 1987) online http://books.google.com/books?id=XlBp10nUTXAC&dq=Gordon+Fee+Bible+commentator&printsec=frontcover&source=in&hl=en&ei=SwLNSu3nA4v6Mf2XlDo&sa=X&oi=book_result&ct=result&resnum=12#v=onepage&q=&f=false