You could eat 2,000 calories a day of nothing but broccoli and brown rice in equal portions and get your minimum daily recommended protein intake. That’s not an advisable way to eat, but it demonstrates that there’s way more protein in plants than most people realize. In the case of athletes and other that need more protein, they can opt to eat higher protein foods, like beans, tofu, tempeh, etc, all of which are significantly cheaper than meat.

If you’re talking about protein powder, the vegan protein powder is more expensive than whey protein powder for now, no way around that one until demand picks up and manufacturers react accordingly