Then look at margin and rough total costs. Then see if this sounds reasonable. Response figures normally bandied around are 1 to 2 percent and followup can increase response. But you can't depend on that. Sometimes one makes a loss in the first place to recruit a valuable customer.
Direct marketing can be a long haul, trying different offers etc.
If you watch Time Life, you see offers for some publications once or twice, then you get lots and lots of activity on one theme, right now it is Ancient Egypt. Readers Offers Direct who are big in the U.K., selling off the page, only make money on about 2 out of 20 products, yet their turnover is millions. Target Online from Target Marketing magazine and DM News will have more about response. They also have lots of articles.