Cheapest: Fiverr Most effective: Google Adwords Man, don't buy Fiverr gigs that promise you traffic. It does not work that way. If something is too good to be true, then it probably is.
Fiverr is mostly automated. You will get 1000s of visitors, but those could be automated bots. If you are looking for Genuine visitors, you will have to work hard on social media platforms and ensuring that you get good visitors through regular blog updates.