A question at this point I might ask is how good does the final estimate have to be?

First, there are multiple applications of accurate estimates.

The unreasonably low estimates would suggest things like "I'm net reducing factory-farming suffering if I eat meat and donate a few bucks, so I should eat meat if it makes me happier or healthier sufficiently to earn and donate an extra indulgence of $5 ."

There are some people going around making the claim, based on the extreme low-ball cost estimates, that these veg ads would save human lives more cheaply than AMF by reducing food prices. With saner estimates, not so, I think.

Second, there's the question of flow-through effects, which presumably dominate in a total utilitarian calculation anyway, if that's what you're into. The animal experiences probably don't have much effect there, but people being vegetarian might have some, as could effects on human health, pollution, food prices, social movements, etc.

To address the total utilitarian question would require a different sort of evidence, at least in the realistic ranges.