Earlier quoted context omitted.
Buy a used server from Ebay that has lots of hot-swappable drive bays. Many can be had for $100-200 and work fine.
I would like to do this, but am worried about the noise. I've heard servers that sound like jet engines. Is anything I can look for to avoid that?
You can probably do a lot better by building a custom one, but that is going to be a lot more expensive. I would love to hear from anyone with experience in this actually, as I'm kind of starting to get fed up with it.
Aside from aggressively controlling the fans, I find the HP and Dell firmwares to be entirely useless, as they all apparently require a web browser with an ancient version of Java. In one case, Java 6. Yeah... this was a terrible decision even 10 years ago.
Another annoyance is that they will mostly come with some kind of hardware RAID card that doesn't passthrough raw disks. Often, a completely worthless one that must be replaced. Even if it's a less terrible one, it will require reflashing if you want to use it in JBOD mode (for ZFS or software RAID).
All that being said, considering that I paid $140 shipped for this HP server 3 years ago, I'm not sure how much I can complain. Setup was a pain in the ass, but once I got it done, it's been working mostly flawlessly since. The only ongoing pain points for me are the lack of USB3, and the fan noise. (I could add a USB3 PCI card, perhaps, but I'm sure that would increase the fan noise even more!)