That's about as good as you can do on such a low budget - pretty nice work, actually.
The one thing I would be cautious about is buying $20 Windows product keys from deep discount gray-market sites. Often they're illegally obtained, or being resold in violation of Microsoft's TOS, like developer or student licenses. They do have a tendency to go poof in 6 months when Microsoft decides it's not a legitimate copy. Probably better to just sack up and spend the extra $60 or so on a copy you know is valid.