You'd be wise to think that, but I actually use Heroku's "Scheduler" add-on, so they just fire up a one-off dyno once a day and run my script. This script just checks the database for the user's it needs to check (paying && valid email) and fires off Twitter API requests for them. If there's @mentions/DMs that fit in with the frequency the user has selected, the email is fired off through AWS SES. Honestly, the server costs for this will be quite low for quite some time. If it takes off big time, sure, I'll re-evaluate the pricing model.