Forum Moderators: skibum
If your 20k hosts are unique users and they turn maybe 8 pages on our site on average (20k x 8 x 30 days) quick math has you at 4.8 mil impressions monthly. If you have two ads on your pages we can double that to 9.6 million. At this size you should try working with a higher tier remnant network: Dedicated, Specific Media, Tribal... which will probably get you $3 or so cpm on avg per month or $28,800k at 100% sell thru on those 9.6 mil impressions.
If you want to go down the direct sales route you'll need to know a lot about your users so you can tell a good ad story to potential clients - Gender, Age, HHI, (your typical Comscore data)
GigaOM just dumped Federated Media for IDG - might be worth contacting them to see about ad representation.