The first hard drive I worked with held 32K words of 12 bits each, so that would be 48 KBytes. It was head-per-track, so it didn’t have any moving arm.
I think it cost us about $6000.
I also recall a business partner spending good money to upgrade our CMP machines from 48k of RAM to 64k of RAM.
Who in the world could possibly use 64k of RAM?