Wow at first I couldn't understand at all how someone would claim that much money just for not being vegetarian. I think there's two important biases here though.

1. "Willingness to pay vs. willingness to accept". This should decrease your actual figures a lot. For example consumers will ask much more money to accept a bad pixel on their computer screen than they would pay to have it repaired. "Willingness to accept" is not really interesting to economists. Basically ask how much they would pay to eat meat for a year if they had a vegetarian diet by default to get around this.

2. Maybe not a bias, but as others said here, vastly underestimating the inconvenience of being vegetarian. It's really not that much of a hassle. Add to that the lower cost and health benefits and the environmental benefits if you care about those and being vegetarian seems like a win-win.

One more thing I'd like to add is that only after turning vegetarian I was first able to understand how severely I had been biased toward neglecting suffering in other species. Speciesist bias you could say. While still eating meat I was simply not able to care about animal suffering enough.