Popular websites devoted to esoterica, personal development, and other related topics have sufficiently large day-to-day audiences, with unique visitors sometimes numbering in the tens of thousands. They keep themselves afloat by selling advertisements and publishing announcements. You can easily make a deal with them to get your banner-ads up on their site. The cost will depend on the amount of website traffic: from practically free to quite large sums of money. A list of such websites can be found in various rankings, which will usually include statistics on how popular the sites actually are.
Taking out such an advertisement isn’t the most effective promotional tool, especially if your activities are limited to a certain geographical location. However, it may be justifiable for distance learning and selling educational materials.