Any specific reason why you'd want to go with NVMEs for your storage, and not just 2.5 SSDs?
If it's performance you're concerned about. I have 3 SSDs in RAID (external USB 3.2 JBOD enclosure), and they perform way better than a single NVME.
For minipcs, have a look at aliexpress. They tend to have the branded options much cheaper than amazon. Trigkey, minisforum, Beelink, etc.