Sure you can use an old computer and host at home much cheaper than AWS / Azure / etc. But on AWS / Azure / etc if the physical machine your VM is running on dies, your VM moves to another physical box within seconds without you having to do anything, within seconds, and without data loss. What is that WORTH to you?
That said, you can get a Synology NAS (easy) or build your own NAS (harder) and run Nextcloud in Docker. In the event of hardware failure (it will happen, it's just a matter of when), you'd just have to bring that Docker container + backing storage back up on the replacement gear.