Why do you think the price of external drives will go up? I've casually (VERY casually) watched the price of storage media for probably 20 years or so. Back in the day, I watched it pretty close. I remember talking w/ a co-worker when the price of PC storage finally went below the $1/mb barrier. I don't remember the time frame when it broke the $1/gb barrier, but I don't think it was more than a couple of years ago. Now, you can get 2tb external drives for ~$100 on sale. 1tb portables (no extra power supply) are ~$100.
There was a guideline (for lack of a better term) that said computing power doubles every 18 months. That seemed to hold true from back in the 50's and 60's through to the current day. I readily admit that I have not looked into the veracity of this, but at first glance, I think it's not that far off.
What has gone along w/ that, is a decrease in prices. I think it's gotten to a point where prices are probably bottomed out, and now you'll just get more for the same money, going forward. For example, you can buy laptops now from anywhere from ~$350 - $700. Sure, you can spend a lot more than that if you want, but you're adding more stuff (more RAM, separate video card, Blu-Ray, etc.). That price point was pretty much the same 2 years ago when I bought my laptop. The big difference between that $500 laptop I bought in 3/09 and what I can get for that same $500 today, is the processing power and more RAM.
The point I'm trying to make, in a very long-winded way, is that in my experience, the price per unit of storage space has steadily declined over the last 20+ years. Baring some external factor that would cause a rise in electronics prices in general, I can't see the cost of storage going up.