Several monthes ago I've bought a banner using non-google advertising broker on a site that has my target audience. It was claimed that my banner will be shown 150k times per month.
Too bad that broker doesn't allow to see real number of times banner was displayed. I was getting approx 3-5 clicks daily on that banner (I didn't track number of conversions).
It costed me $50/month. It seems more experiments are needed with that broker (it has too many sites in database to choose from).