This article makes a point about premiums for non-GM but another important economic factor is market loss.

According to an economic study of GM crops by Australia's Rural Industries Research and Development Corporation (RIRDC), "the US share of the EU's maize imports has fallen to virtually zero (from around 2/3 in the mid-1990s), as has Canada's share of EU canola imports (from 54% in the mid-1990s). GM-adopting countries have lost market share to GM-free suppliers".
http://www.geneethics.org/Default.aspx?tabid=85
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Japanese pay premier price for GM free canola
ABC (Australia), 01/02/2006 http://www.abc.net.au/rural/content/2006/s1559754.htm

Grain growers on Kangaroo Island are receiving a premium price for their genetically-modified (GM) free canola after signing a deal with a Japanese company.

After four years of negotiations, 18 growers on the island are exporting a trial shipment of 2,000 tonnes this month and hope to double the tonnage next year.

Derrick Johnson from the Kangaroo Island Canola Company says the Japanese approached growers because of the island's GM free status.

"The idea is that the canola be GM free which flys in the face of all GM proponents which say there's no premium for non-GMO products," he said.