Ask HN: I want to start a vertical ad network, any recommendations for tools?

I'm starting a vertical ad network in the smartphone apps space (developers and development studios would come to us to promote their apps on our network of app review websites).

I have a portfolio of websites to seed the network with, and the aggregate monthly pageviews is already non-trivial. So no problems, there. I also have a reasonably strategy to acquire advertisers.

I'm looking for recommendations around: 1. Which Ad server to go with 2. Back-office services: billing and payment distribution to partner publishers

I've looked at Adify (very pricey setup fee and no trial), and have applied to the iSocket beta.

Anyone have any suggestions or experience with something like this? Thanks!