500GB did NOT cost $100 ten years ago. They were much less common then, and were a lot more expensive. They were very new, after all. Most computers didn't have hard drives anywhere near that size - I got a new computer around then which had a 160GB drive, and that was pretty standard.
...Actually, thinking back, it was probably even later than that that I bought that PC. I'd only had it for ~4-5 years tops when I bought my current desktop in 2009. And 500GB drives were still really expensive when I bought a 300GB drive for it a year or two later, so it's probably closer to 5 years ago at the earliest that 500GB drives cost $100. You also need to take inflation etc into account, of course.