It will, but the upkeep is extremely low. It takes roughly 15 minutes to set up a DigitalOcean box with Dokku (I think they can even install it automatically for you if you set up a cloud-init script). What I'd honestly do if I was managing a LOT of sites is write a tiny bit of terraform or something to stand up all those sites, and then delete and recreate all of the servers on like a quarterly basis so they all get patched. Slightly more upkeep, but an 8gig/4CPU DO box costs like 48 bucks a month, which is a hell of a lot better than Heroku at that price point.