If you are concerned about having to upgrade every year then I suggest sticking with Bootcamp or Virtual Box. I believe that Parallels will release an update so you can run Yosemite with Version 9 but with the next OS after Yosemite you will have to pay. Same with VM Fusion. Parallels have been releasing updates to go along with the developer updates released by Apple to the Yosemite Beta.
In the end though you will pay somewhere down the road. This is always a debate about how you have to pay so much to update Parallels or VM Fusion everytime Apple brings out a new OS. This is why I suggest you go with Bootcamp or Virtual Box. Both are free and will never cost you to upgrade.
Even I flinch with the $50 upgrade price. Only software where I struggle with the upgrade price. Would not be so bad if it was only $10-20 each time for average consumer.