Advertisement Campaign clarification

Hey guys ,

From tomorrow , i will start advertising from either facebook or app brain , i’m a little confused with the terms and the way how it works…

First you have a daily budget and ou can fix your ecpm , say i have a budget of 10 $ and i have an ecpm of 1$ then i get 10,000 views?

Secondly , regarding the cpc , is it viable for a free app ?

I have a free app with ads and its paid version for 1.99 usd , so I want opinions from people about which model worked out for them , because i dont want to be shooting in the dark…

PS- i have 600 usd to spend and I dont know how i should be distributing between free/paid app or just pay to advertise any one of them…

Thanks,
Jeet