Using a hobby-dev instance and hobby-dev PostgreSQL database ($14/month), you should be able to handle up to about 100k events/day, with approximately a 100 day history.
With the next step up, 2-3x hobby-dev instances and standard-0 Postgres ($64/month), you should be able to handle about 1M/events/day with over a year's worth of history.
If running costs are a concern, AWS is likely to be the cheapest cloud option, especially if you can commit to buying reserved instances for a year. This does come at the cost of ease-of-deployment.
If you've deployed on AWS, please let us know roughly how much you're spending roughly so we can improve this guide.