I don't know about the $50 per day part but pretty much any charity or volunteer organization counts on large numbers of usually trained part-time workers showing up to get the job done.  It is why it is referred to as being a volunteer position.

The other part of the equation missing is that unions depend on their membership to exist or more specifically on the union dues to exist.  I am willing to bet that if the volunteer departments were kicking in dues this would be a non-issue.