On the other hand if you're willing to ask for help there are plenty of freelance IT admins who would set up a digital ocean box with the DIY equivalent of Heroku.
I have read similar comments to the ones here about scaling and cost, so I might bump into that at some point.
Leaving a box with no monitoring and no on-site skill capable of fixing it is a bad idea. That box will explode at some point and it's going to explode at the worst possible moment, and you'll loose tons of business (and/or data) while you scramble to get someone to repair it.
Unless you have people ready to jump in and fix it should it break, don't risk it and just let Heroku handle it.
Also, just because you use Heroku for your app servers (dynos) doesn't mean you have to use it for everything.
I think the main competition for Heroku these days is AWS and GCP. The workflow for deploying directly to managed cloud services has improved drastically over the last few years, so you might not need the niceties that Heroku offer.