As much as possible
Hi Kevin, that's a tough question to answer for anyone. There are so many factors, including how well your visitors are targeted to the advertiser. If you want a suggestion, which is all it really is, I'd go with 50 cents or less for ppc and anywhere from $10 or $15 up to $100 per month for cpm based on the number of impressions you have.
My approach instead would be to figure out what your competition is charging, and use that as a guide initially. Then once you have advertisers, get to know them and how your traffic is converting for them if at all. Charging anything, even a dollar, for advertising that doesn't convert isn't going to work for you or the advertisers.