Mobile Game: In game advertisements

I'm an Indie game producer working on my first project. We are making a low rent platformer intended to be released on iOS and Android. I'm looking to find some information on in game advertisements. I like the idea of selling a full ad free copy of the game and offering a free copy that contains in game ads to generate revenue. I'm looking to find out what to expect as far as revenue generated from ads and are there marketing companies I should talk to about partnering with that will find customers to place their ads in our game?

Any advice would be great!

Thanks,

Neal