Well, psy, as you suggest, we should think outside of the box ;-)

Lets see what you get for this 1$:

• Your message is kept forever. I don't think there is any other service in the world offering you anything like this.
  
• Lowest possible rate. Any price divided by eternity is mathematically 0 $/month.
  If it was for 50 years only, it would have meant 0.0017 $/month. Affordable, isn't it?
  
• Proof of time - you can easily prove that this message was written before it's timestamp.
  

But that is not the main thing about the bitcoin message at all:
Where else do you get a backup of your data in 100,000 locations uniformly distributed all over the planet (is there any bitcoin user in Antarctica)?
Even in the most secure services, e.g. Amazon S3 you may have your data in 2-10 locations. Bitcoin message service offers here a backup which is 10^5 times stronger, not to mention that it is kept by 100,000 different people.
Another important note is that the message cannot be erased (with any other service, e.g. Amazon S3, a government can easily order to delete the message).

Let's go one step further:
If the civilisation is destroyed or if simply WWIII starts, the messages of the bitcoin message service will be the best survivors, as there are so many scattered copies of the messages. Soon more copies than the bible ...

You have mentioned digital tattoos. They are also an option, but the service is meant for special information publishing needs:

• Anonymous publish of data (leak sensitive information securely and directly using the p2p network).
• Proof of owning information with a timestamp (e.g. patents and other intellectual property related).
• Keep data that cannot get deleted or lost.

Hey, when I look at the service this way, the price of 1$ is way too low :-)
Actually it is no where even close to the development and running expenses ...

BTCmsg,
at your service.