As previously mentioned, Purgatory Comics is now available to rent or own on Vudu.com. It's $19.99 to own in HD and $14.99 to own in SD. Or, you can rent in HD for $4.99 and rent in SD for just $3.99.
What's pretty call about Vudu is that aside from viewing the trailer, you can also actually watch the first 2 minutes of the movie. You can find it right here.