8 track HD
A friend of mine wanted a backup hard dive (500 GB) but didn't want to spend $80 on it, so I went digging online.
I bought a 500 GB internal hard drive on sale online for ~$20 used, (list ~$80 new)
a $4 dollar SATA-USB cable,
and found an 8-Track Tape.
with a few internal modifications, the hard drive fits inside.
Total Cost: Under $25