Not the cost, the easy risk of malnutrition and requirement of supplements for B12, iron, D, iodine and omega-3...
The majority of vegans also have difficulty getting all of their protein/amino acids. I actually use a vegan protein powder due to lactose intolerance that solves this issue, but it's an extra cost not everyone can cover.
Not to mention the elevated risk of Diabetes due to the high carbohydrate diet most vegans have.
Or... You can just eat a chicken breast and solve all of these issues.
Running shoes last 300-500 miles, and can last even longer if you're just walking in them.
Brooks' Gost 15 are my current pair and hold up more than a year.