So, where's the truth? All the studies (by pro- and anti-labeling groups alike) rely on assumptions. One assumption often made by pro-labeling groups is that the government costs of monitoring and enforcement are essentially nonexistent. As the Washington study suggests, however, that's unlikely to be true and these extra costs will either manifest themselves in higher taxes or higher food prices, depending on how they're funded and people respond. Pro-labeling groups are right to suggest that the physical costs associated with changing the label are relatively small and close to the "cost of ink." The much bigger question, and where most the controversy arises, is how food companies will respond to the label. If they respond by seeking to source non-GM crops, the cost implications could be quite significant, and this is how we arrive at numbers like $1050/family (the new Vermont study also assumes manufactures will have to comply in all states not just Vermont because of possibility of liability if one of their unlabeled products sold elsewhere unwittingly finds itself on a store shelf in Vermont). If instead food companies shrug their shoulders and just slap the label on all their products, the costs are likely closer to just the physical re-labeling costs and the government oversight and regulatory costs.
So, how will retailers respond to the label? My guess is that the answer is somewhere between the extremes: some will dis-adopt GM and others won't. Thus, the expected cost should be calculated by multiplying the costs of disadoption by the anticipated likelihood of disadoption. I find it a bit hard to believe that all retailers will fully move away from GM content to avoid the label (i.e., that the probability of full disadoption is 1). Why? A lot of consumers are unconcerned about GMOs and many more have no opinion on the issue, and thus there will remain an incentive for food companies to remain cost competitive. Also, the US is going to produce a lot of GMO corn no matter the labeling policy because around 40% of the corn crop goes into our gas tanks as ethanol and most of the remaining corn crop is used for animal feed (and animal products are typically exempted from the label). These much larger demanders of corn, as opposed to comparatively small demands for high fructose corn syrup or corn starch, are likely to drive the market for corn.
So, all this would suggest that $1,050/household/year is an upper-bound estimate associated with the mandatory labeling law. And, I think that's true, except for one thing. The potentially much larger (and admittedly more speculative) costs could come about if we create a culture and market environment that is hostile to the introduction of biotech crops and crop technologies. What future innovations will we forego if retailers chose to disadopt? We may never know, but it would be a mistake not consider these opportunity costs.