You might get reasonably current, but accurate is much more difficult because of all the contributing factors that go into it. That said, you can start with what you have access to already. If you know that your offers in a sphere are taken by 20% of the people who elect to view them, that can be a starting point. If you visit trade shows and you ask enough people you can get a sense of conversion rates online. They vary a lot based on the the reasons (and search terms, or prompting) why users choose to a view an offer. Once you get a rougfh estimate of the conversion rate, visit adwords or get a temporrary sign up at semrush or spyfu and enter a seed keyword for your industry segment and find out the average cost/click. - do the math - 20 bucks/click on a 20% conversion rate would be a $100 CPA