One thing I haven’t seen mentioned is looking at Facebook Groups. The advertising can be weird because it is somewhat of a grey area, but most Facebook groups pages are run by companies or moderators who are looking for a little extra cash. They will add you to their group and let you post a certain amount of ads per day. You have to make the posts interesting and provide value to the group members, as more engagement will increase the reach of your post.

On a side project last summer, I was able to work with a company running education niche groups. To join 10 of their groups (total reach probably around 30k audience) was $500 per month billed on PayPal. Could make a post per day in all 10 groups, so 300 posts. The conversion rate was better than any other paid advertising we had tried and the targeting was much easier.

It’s easy to get started: find a few Facebook groups you might be interested in joining, go to about this group, add the admin as a friend/send a message request, and ask about advertising opportunities. Be sure to show them your project, and why you think it would be beneficial to their audience, that will help your case!

Also - have you thought about going to teachers with your product (assuming it’s compass letters from your post history), getting them on a free subscription, and hoping the kids go home and tell their parents they want to get the letters too?