I want to start building links again, but only from websites, pages and blogs which have

1) Traffic niche related or semi niche related.
2) Rank themselves for good and related keywords or show sources proving to me that they actually get visitors.

Need to be free or cheap.

I have a few questions:

Have you ever bought those types of links? How did you find them? And how much did they usually go for.

Any advice would be appreciated.

~ Mike