Mild DIY NAS for Linux or TrueNAS?

Hi there, I have an old LaCiE NAS that the company stopped supporting many years ago. But fortunately I found a wiki with instructions for unlocking the bootloader and installing normal Debian for armel/Kirkwood, and it's now running Buster with OpenMediaVault. It's a perfectly reliable system now, but it won't last forever and it's extremely slow, so I'm looking at options to replace it. But I'm wary of the proprietary operating systems that the NAS makers throw over the fence and stop supporting after a few years. I would strongly prefer something with no bootloader restrictions that lets me install a mainline Linux distro like Debian or even TrueNAS with no hacking. I'm a longtime Linux user and I enjoy setting up my own system on the software side, but I hate messing with hardware and at most I would be willing to install some hard drives. I just want a 2 bay device, and I don't want to deal with external USB enclosures or cables. Since I have very low requirements in terms of hardware specs I would like it to be as cheap as possible. Any recommendations for low priced hardware that an run Linux or TrueNAS? Thanks a lot.