This is what I know from personal experience...
1. the price used to be $250 for hd owners.
2. then the price went to $1000
for hd10 (release 10/20/11)
3. then the price went to $600 for hd11 (release 6/21/13)
4. Now the price will be $1200 ($600 per year and upgrades come roughly every 2 years)
I do not like this.