I've been a veggie for over 30 years now, and also have no fundamental issue with the prices I pay when eating out, as most of the underlying cost has little to do with the raw ingredients that make up a dish.
I imagine Yes Chef could give us an idea about how the pricing of menu items works.
They - https://theburgershopco.uk presumably - might be buying that veggie burger in: https://www.brake.co.uk/meal-solutions/meat-free-vegetarian/burgers-grills-other/burgers/brakes-spiced-butternut-squash-quinoa-burger/p/122509
Regardless, only a small