I submit that cheap traffic can be profitable. IF: you find the right targeted location. IF: you approach it with effective marketing copy. If you don't know how to find highly targeted traffic sources for your product and if you don't know how to approach those sources I agree that you won't find much profit from cheap traffic. In the end you'll find that the real path to success is traversed by using both paid and free traffic.
Guest post on other blogs, social media. What sort of content do you need traffic for? It would be easier to advise