Ok, so if you want to do a bunch of drives in a box:
https://pcpartpicker.com/product/FhPzK8/gigabyte-mw50-sv0-atx-lga2011-3-motherboard-mw50-sv0
https://pcpartpicker.com/product/yFWJ7P/crucial-bx500-4-tb-25-solid-state-drive-ct4000bx500ssd1
However, that's expensive. I would go with spinning disks.
If you want to bring the cost down more,
You can drive the price down more by buying a used system.
The pile of SSDs will be easiest to stuff into a box.
You will need to get creative with cooling.