Wow, what timing. Just last night I came across the greatest website... A perfect solution to your question.
Duane Marx over at:
http://www.provenadsecrets.com
has put together the best resource site I've ever seen for this sort of a thing. He's spent unknown tens of thousands on advertising in various ezines, and shares all the numbers and ads and everything he's found each and every time.
I'm loving it... The ezine ads section alone are 100x worth the price of admission, but it goes on to give reports on all other forms of online advertising too!
Enjoy!
Luke W Parker
the Home Biz Factory
http://www.homebizfactory.com