One of the best alternatives I found is using dokku with a cheap VPS. Dokku even has herokuish buildpacks and supports (automated) deployment of docker images etc. On top of that dokku is open source with a very helpful community, total cost: 0$.
Not looking back at all.
I tried Dokku out but I didn't like the lack of GUI, I wrote in another comment but I've been using Coolify (https://coolify.io) as a great alternative with a built in GUI, also free and open source.
https://dokku.com/