Most of our clients are not knowledgeable enough to understand clickthrough rates et al, and prefer to work with us on a monthly basis price structure. Currently it's at $1000/month for a front page banner, and $500 for a detail page inside. I looked at the number of ads it was served, and depending on the site, it averages maybe 50,000 page views/ads served. So we're talking about $20cpm.
Now I know that depends on the industry and targetting, but can someone tell me if $20cpm is around the range, or this is really expensive (from a clients perspective - good for us;)) and cpms usually go for $5-$10?