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

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 ---(looking at the US)

Based on primary data (n = 1040) collected through an online survey, representative of the Portuguese population, through logistic regressions, it was possible to conclude that plant-based consumers, particularly vegan, are associated with lower food expenditures compared to omnivorous consumers. In fact, plant-based consumers are shown to spend less than all other consumers assessed

https://agrifoodecon.springeropen.com/articles/10.1186/s40100-022-00224-9

Depends on your region. Meat is never affordable from the supermarket and in-city but in areas with an active local fishing industry for an example, fish can be one of the most cost efficient sources of nutrients if you purchase them directly. Saved my life when I was going through poverty.

One should note that vegetarians exist and those tend to be (generally) more affordable due to having a bigger variety in choice while also cutting out the expensive meats. Also generally more accessible than a vegan lifestyle, is not suiting every person's metabolism. I'm now a vegetarian purely because meat is unaffordable to me currently (I moved away so no more cheap fish)