I've recently discovered the Caddy server (https://caddyserver.com/), which makes SSL and application proxy deployments super easy. Like, 2 lines of config:
domain.com #uses the domain to automatically set up SSL with Let's Encrypt
proxy / localhost:8080 #redirect everything to Arc on 8080
I will say that Arc runs a bit resource intensive, and the slightly slow boot times mean you don't want it to have to re-launch because of infrequent requests. I don't know how well it would work on Heroku.
Also, some VPS services like vultr.com offer $5/mo nodes that have more resources than what you get from Heroku at $7/mo anyway.
I should mention that if what you want from Heroku is their deployment process, you can actually replicate some of it pretty easily with Caddy (though I have not done so yet myself; I plan to soon...)
Specifically, they have support for automatically fetching code from git and running a command in the repo, either periodically or triggered by a webhook: https://caddyserver.com/docs/http.git
That doesn't get you the app ecosystem that heroku offers, but you can get a lot of that pretty easily via docker and docker-compose now.
