Since no one has mentioned it, I'm a big proponent of Positionly. They're very price efficient and if you've got some patience you can get an amazing deal. I got suckered into the autumn deal iirc.
I used to use Positionly and it's pretty affordable at $15 a month for the base plan. Also if you're a "startup" then there is a six month free plan https://positionly.com/startups