Let's say you're running a half-page ad in a single newspaper or magazine. Why not cut the size down to four, 1/8 page ads in four different publications and run them there?
As long as your ad is well-designed and well-placed, you might be better off. You might see a better response with several smaller versions of the same ad in several different publications than one big ad in a single publication.
You never know till you try... :)