This will depend on a number of things, including how many ads you place in your newsletter, what your competitors are charging, and how tight your target market is. It is in your best interests to research what similar ezines are charging for ads. One great place to do this is at the Directory of Ezines . This excellent directory provides very detailed information on advertising rates for hundreds of ezines in every imaginable category. A searchable database is provided for fast, convenient access.
Classifieds are always the cheapest, followed by sponsor ads and then exclusive mailings.
Make it easy on a potential advertiser. Tell them what they want to know, and keep things simple and clear. For obvious reasons, potential advertisers would like to know how many people their ad will reach. It's nice to know WHO they're going to reach with their ads. Obviously, if you don't have this type of information, just leave it out - don't make it up.