Firstly, if you don't have a list for the targeted traffic you are generating you will be stuck with ever increasingly expensive paper click mailing list advertising as an option. Pay per click advertising may have been a good model in the past, but because of increasing competition the price has gone up tremendously. It is going to be hard for the small time Internet marketer to compete with big corporations who are willing to spend big for keywords.
Another thing you will have to depend on to get targeted traffic if you do not have a list would be word-of-mouth advertising as one of your main online marketing tools. Word-of-mouth advertising should be a tool you are already relying on, but mailing list you don't want to rely on it solely. You never know when word-of-mouth may turn negative or when it may dry up altogether. Plus it's going to be a constant battle for you to stay relevant and on the minds of people in this way.
Lastly, you have to hope you're able to ultimately beat out websites that have put in possibly years of work to achieve their top search mailing list engine rankings. What this means is you will have to work to build several hundreds if not several thousands of back links to get good rankings. You have to make sure you keep updated with changes to search engines along with trying to establish domain authority, which can take years.