It’s worth noting that in countries like US, it’s really only things like beyond burgers and impossible meat that cost more. It doesn’t require eating those for a plant-based diet nor are people typically eating those every meal, is why plant-based diets generally have lower costs

Compared to meat eaters, results show that “true” vegetarians do indeed report lower food expenditures

https://www.sciencedirect.com/science/article/abs/pii/S0921800915301488?via%3Dihub

It found that in high-income countries:

• Vegan diets were the most affordable and reduced food costs by up to one third.

• Vegetarian diets were a close second.

• Flexitarian diets with low amounts of meat and dairy reduced costs by 14%.

• By contrast, pescatarian diets increased costs by up to 2%.

https://www.ox.ac.uk/news/2021-11-11-sustainable-eating-cheaper-and-healthier-oxford-study