Any campaign can be broken down in terms of cost per thousand, and if you are seeking a direct response, it should be monitored according to cost per response and also cost per conversion. Advertising cost per thousand includes cost of origination (design), production (printing if relevant) and media (such as local radio, display advert, list procurement and postal fulfillment). Generally you will pay a higher cost per thousand for better targeted methods, but in return you should expect a higher response rate, so the cost per response can be lower than cheaper methods. Choose advertising and publicity methods that suit your targeting. Organisations selling advertising are able to provide a lot of information about their readership/audience, and you can look at other advertisers that repeatedly using various media to gauge how effectively it's working for them, which will provide some clues as to how well it might work for you. Are they targeting the same audience as you? If so you it's an idea to call them and ask if the particular advertising method is one they's recommend or not.
Getting and building evidence of advertising effectiveness is a vital part of decision-making, and managing your advertising and marketing mix. Why guess if you can base decisions on experience and previous statistics and data? Sophisticated advertisers only commit to major programmes after accumulating response data from pilots and previous campaigns. They avoid guesswork, and so should you. Any large scale activity must first be tested and the response measured for quantity and profile.