I do publicity as a profession. I have to. If I did no marketing I would not make any progress. Once you do effective, easy marketing things change dramatically. Simple press releases, utilize free calendar services of local media, get them human interest stories for features, invite them to events, Never let anyone go with out a cheap and simple handout or song sheet with information. Plan events ahead. It does not have to be expensive at all. Most media outlets have e.mail contacts. One can send out pr to hundreds in one e.mail never been easiier. Go to schools.
The most important pr is making sure at all points that there is the easiest access to the music. Lower or remove costs, be willing to expand. And take advantage of the suggestions above. Dont know your budget but I find quarter page flyers economical.

You an always provide song sheets at cost. I used to keep in touch with my volunteers - at one time 100 or more by gluing flyers on stampped post cards which they supplied.

Lots of free ways. Access however is an important step.

You dont have to make it a lesson. That is an option and sometimes at the right venue it is something for which there is demand. You are correct one has to combine it with entertainment but as a teacher I have hundreds of methods that can slip in education painlessly- all in training but not rocket science. Lots of on line ideas too many to detail.

Teaching people to listen is an important task. This takes only a few words of introduction perhaps. However old style folk music sung in whatever way coming from the heart and soul does its own work.

Conrad