Scheduling cron jobs

I want to develop an app on which a user can register for alerts( multiple) so that whenever the fare hits below some threshold, he gets a notification. Fares are fetched from a third party website.I want to do this on google app-engine.

Now from what i understand , i need a process running 24/7 which checks the fares at say intervals of 30 mins and send out a notification whenever it hits below the threshold. Probably the cron job of app-engine can be used for this task ? But at max 100 cron jobs can be scheduled, what would be the better way to this. Also having a process for each user would be wastage of resources, what would be better scheduling algorithms for higher efficiency ?

You want to schedule a single cron that runs every 30 minutes and throws an item onto a task queue. That single item on the task queue would then be able to go through all your users, and generate tasks to fetch whatever you need in the background again. Two important things:

1. You want the initial cron call to return as quickly as possible, as URLs have a 60 second deadline.
2. Split up any work into separate task queues to achieve above and also iterate through data sources and/or users.

Based on what you're explaining, you can use push task queues: https://cloud.google.com/appengine/docs/python/taskqueue/overview-push