we'll easily see 3-5TB hard drives being $200 at most in 10 years.
Literally not even an argument.
Especially seeing as you are only off by a pessimistic decade:
http://www.newegg.com/Product/Product.aspx?Item=N82E168221459724TB. Under $200. Today.
10TB is shipping in volume, and next generation will be 14TB. Welcome to essentially free blockchain storage.
You're welcome.