Any good paid blogging sites?

Recently I have noticed that some of my competitors are ranking above me for some keywords, because their backlinks are coming from various blog posts. Most of these blogs are having posts that link to different sites, so they must belong to a network of paid blogging sites.

I'd like to know which paid blogging site network is good for posting my articles for quality backlinks, and at the same time is cost effective. I'd appreciate your sincere replies.

Thanks.:drinking2: