Orico has a 4/5 slot USB3-10gbps DAS box, which can daisy chain up to three boxes.

Get 6 boxes, daisy chain them as 2x3, connect to a powerful-ish NUC box. Install TrueNAS on it. Use the SATA port for the OS, leave the NVMe slot alone, add a 2-4 TB good SSD.

Set the SSD as a cache to that 30 disk zRAID2 or zRAID3 pool. You can have a kick-ass enthusiast level NAS box which will beat many Synology boxes with a big clue bat...