"No protein/only eggs" should be an option, but the extra cost probably can't be helped. If they can buy meat sausage in bulk at a lower rate, that savings can be passed on to the customer. If their plant based sausage can't be bought in bulk or doesn't come with the same savings to do so, then that cost must be factored into the product to maintain margins.
Stuff like this is infuriating. Yes there are people who cannot imagine not eating meat, my father is one of them… but he also admits he only eats meat once a week at most.