Last time I used Heroku for a real project, I just put the database somewhere cheaper (if i remember correctly, Azure). With proper encryption+authentication and a bit of strategic caching, it was fine.
I use Heroku for an internal app and found their hobby Postgres sufficiently flaky that I now use RDS in the same region. For $20/mo on RDS, we get more than the $50/mo tier on Heroku Postgres and the latency isn't much different.