Personally, I would look at a cheap 4U 24bay supermicro CSE-846 off ebay or some other refurbish/reseller if you have room to place a 4U rack mount server somewhere (this is what I did for my home). You can sometimes find barebones systems in the $200-300 range, but expect that they are really something that you will basically be gutting, and need to usually get your own motherboard/cpu(s)/ram and sometimes even power supplies (I recommend getting your own power supplies anyway unless it comes with the SQ versions in the first place as they are the quiet ones, but you might need to change out some internals as one of the three different power distribution boards does not support the SQ version power supplies (without modifications... but I would recommend just replacing)).
Replacement parts are readily available since there was such a huge supply of these cases in the market and as an enterprise chassis, everything was replaceable, from power distribution, to fans, to SAS/SATA backplanes, etc... People have also placed standard ATX power supplies in the chassis, but there are limitations (no mounting holes for a standard power supply, but you can simply use velcro/dual lock/doublesided tape and you need to remove the internal PSU cage for the hot swap PSU's it is normally configured to use).
You can many times find cheap used barebones server setups (motherboard, cpus and ram). Heck, I have 2x 6c/12t Intel XEON low power CPUs and 192 GB ECC RAM with a supermicro board (with out of band management and LSI SAS3 controllers) in my setup, that cost me ~$300. This setup has room for 24 hot swap 3.5" drives (or you can use 2.5" as long as it is a SATA/SAS connection). Internally you can can an optional cage for 2x 2.5" drives (which is what I use for my base OS, which is really a hypervisor for running VM's and I run several VM's, including TrueNAS for handling my storage as direct passthrough).
Yes, there are newer chassis than the CSE-846 and you will see many of them for cheaper as well, but the 846 is the one that you can remove the fan wall and replace it with 120mm fans that run MUCH quieter (as well as fit tall tower CPU heatsinks, and the ATX power supply with simple modification). If you don't mind the noise and the other benefits, feel free to look at some of those other supermicro chassis like the 4U 36bay CSE-847.