I'm not sure how many paintball guns you get for $300,000.
The benefit is hopefully fewer incidents like this where US border agents shot across the border, killing a Mexican child in Mexico. http://www.foxnews.com/world/2012/10/12/us-border-patrol-age... (Throwing rocks at people is obviously illegal and needs to be dealt with. I struggle to understand why extra judicial killing is an appropriate punishment for this crime.)
I grew up playing paintball. They're just liquid balls in a thin plastic. With a jacket on they won't bother you too much. At 50 ft the rental guns will start to stop breaking, especially on soft clothing. At 100ft the best guns you can buy will start to stop breaking even on bare skin. I have a hard time imagining them being effective outside of a very small set of circumstances.