People on plant-based diets tend not to eat a ton of plant-based meats, and lower income people are esspecially less likely to be relying on them because of cost?

I don't follow what you are saying about not being applicable to the US, and UK. Those countries are the modeling study most applies to and shows lower costs?

Additionally it's worth mentining if we look at other data, lower-income people are most likely to be vegan and vegetarian

Meanwhile, lower-income Americans (7%) are about twice as likely as middle- (4%) and upper-income (3%) Americans to be vegetarians . https://news.gallup.com/poll/510038/identify-vegetarian-vegan.aspx