JonD
I take it you don't have a dedicated PC running Sonar 7? A hundred bucks could probably get you a decent XP system off Ebay. If you live in an urban area, you could probably pickup the same system at a thrift store for less than $50. Once all the final updates are installed, there's no need to even have it online (Wouldn't be a good idea anyway).
If OP was going to spend any money, I would suggest puting it towards upgrading Sonar rather than on antiquated hardware!
Not sure if it will run on win 8 but don't know particularly of any reason it shouldn't. Why not just try it?