CPM or fixed price?

best options for advertising

[steakaphagus]

Just about got my site content done, now looking at how I might actually one day make money....
My site is <snip> info based, about 100 pages in all, based in UK. I plan to bring in advertising as side-banners, but try to keep it to medical related companies only.
Any advice on whether I should charge for set fees per month for the advertising, or CPM? (considering that I have minimal marketing budget and site is new, so traffic will be slow to build up, making CPM slow to pay. Conversely, fixed price may be hard to increase as site gets more traffic)
Any views on how much to charge for fixed price or CPM per month?

[edited by: lorax at 7:43 pm (utc) on Sep. 23, 2008]
[edit reason] details aren't needed [/edit]

[jimbeetle]

Whether you charge a fixed price or CPM advertisers will think in CPM anyway as that's the underlying metric used in banner advertising. And the bottom dropped out on CPM prices a few years ago, making it a not very good solution for low-trafficked sites; most would be very lucky to cover the cost of a beer (and a small beer at that).

It might be best at first to look into a CPC program such as AdSense or something similar to see what they return.