You know, I've run those numbers too, and I came up with an absurdly high number...
I looked at the growth rate of hard drives over the past 20 years, then drew it out another 20 years...
25 years ago, $200 wouldn't buy a hard drive, but we did have 10MB hard drives (abit for a lot of money)... They cost $2,000 (for the sake of discussion) So that works out to $200 per MB.
Today we have 400GB hard drives (for amazingly little money)... So $200 for 400GB works out to $0.0005 per MB.
That is actually a jump of 16 BILLION times the space per dollar.
So what happens if you run that out 25 years from now? You get a silly number, that I have a hard time thinking of...
6,400,000,000 TB of storage space for $200
You have kilobyte, megabyte, gigabyte, then terabyte. What's next? Google to the rescue - the next four are petabyte, exabyte, zettabyte, and yottabyte. Now you know.
So that works out to 6.4 zettabytes!
Or enough to store almost a TRILLION dual layer DVDs! (the actual number is 752,941,176,470)
Now I don't know if we'll have that much storage in 25 years or not, but damm that's a lot of space!