Depending on your site, you may need to pay if you want a reasonable ranking. You can spend a lot of time and make a study of search engine indexing and ranking and tinker with your site to improve your ranking, but it tends to be a full time job with no guarantee of results. Paying is easier. (However, it still doesn't guarantee you a top listing.)
If you just want more traffic to your site, check out the dozens of ways to promote your site. Search engines are only one way to drive traffic to your site.