Cheepnis is a small library that makes it easy for Heroku-based applications to spin up worker processes when needed, and shuts them down when they are finished.

Rationale:  Keeping a worker going continuously costs around $36/month at the current rates. This is reasonable for commercial applications but for hobbyist and free sites it is quite expensive.  If all you are doing is sending mail a few times a day, this would keep the cost down to the $1-5 range.   

Install:  
Assuming you are already running your app on Heroku:

Put cheepnis.rb in your applications lib/ directory.

Use the Heroku gem by adding this to your config/environment.rb file
  config.gem 'heroku'

Set the Heroku config variables so your app can modify its own settings:

heroku config:add HEROKU_USER='you@somewhere.com'
heroku config:add HEROKU_PASSWORD='yourpassword'

Use the credentials that you use to log into the Heroku website.  

Use:
Call Cheepnis.enqueue(obj) in place of Delayed::Job.enqueue(obj)

Reference:
http://docs.heroku.com/delayed-job

Caveats:

It's within the realm of possibility that something could go wrong with the machinery that shuts the worker down after all jobs are processed; which could result in more charges to your account.

It's also possible that the Heroku people may take a dim view of this kind of usage, although it's not doing anything except using their API.  Personally I think they should make it easier/cheaper to do this kind of thing for low-volume applications, but it's their business.