If you had the luxury of internal, you’d be looking at $400 for a Highpoint or equivalent + x4 2TB NVMEs at between $200-250 a piece for about the $1500 mark.
For external, you’re in the $2100 range for 8TB external NVME storage.
If you are super desperate to keep costs down, I wouldn’t advise it, but you could roll your own with this…