I'm pretty sure my upgrade price for Windows OS's has been 99$ since 95 with the notable exception of when Vista came out and I "downgraded" to XP Pro for the sheer sake of my sanity. I think that was $179, and I was miffed.
I bit on the $59 upgrade from 7Pro to 8 because I had to buy a new computer for an 84 year-old man who lives out in the middle of 120 acres of family land, and DSL finally hit the area. And you really need to be online to "get" Windows 8.
I have a computer that's over 5 years old, and 8 has improved its performance. Dunno why and all results will vary, but anyone who buys 8 for 200$ should have a financial advisor. Really.