As 1UP points out, it's not hard to find much of the series online for free viewing (including the official RvB website, which features some episodes on a rotating basis). You can also purchase a nineteen-episode DVD for each season, with bonus features, from the Rooster Teeth store for $20.
Still, one dollar might be that golden price point where, like Apple found with iTunes store, consumers don't mind paying for the convenience of downloading content. We'll probably have an indication of how well the price is working with what we presume is the inevitable release of episodes six to 10.
[Update: math error with DVD.]