The first hard drive I ever bought was a 20MB Seagate ST-225, paid $500 for it in 1984 which works out to $25 per MB. I thought it would not be possible to ever use that much disk space. Nowadays we pay less than $0.10 per GB. Times sure have changed.
In the late '70's I was a tech at IBM working on the 3350 Madrid disk drive. It was as big as refrigerator, required 220VAC and had 2 HDA's (Head Disk Assembly) that each held 300M. I think they cost $20-30,000 and were typically installed in strings of 4. A string of 4 only stored 2.4G. It was considered the industry leader back then.
String of 3350's:
I have a 16G thumbdrive that's about the same size as my thumbnail that I carry on my keychain that I bought it for $15. It can store more than 6 strings of those old 3350's!