Checking diskprices.com - https://diskprices.com/?locale=us&condition=new,used&disk_ty... - there's a cheaper outlier for DVD-R, then it's 25GB BD-Rs for a bit.

LTO tape can be cheaper, but the cost of the drives has long been an obstacle to dabbling.

Yeah, the prices don't seem to be correct. New 16TB HDD for $200. DVD+R 25x pack for $2, etc. Clicking the links shows different prices on amazon, etc.