HDDvsDVD

DVD - 4,700,000,000 bytes capacity - 24 cents
Real world capacity - 4,100,000 bytes

+ 1 sleeve per disk ($3/25 for Tyvek sleeves) + storage space ($7 for 100 sleeves)
is about 9.4 cents per gig to store (ideal)
10.8 cents per gig to store (for real)

Hard Drive - 400,000,000,000 bytes - $90

+ enclosure ($30)
is about 32.2 cents per gig to store.