With our business local radio is the best bang for the buck. We had a remote once to get people to know to get to the show room. I know you have government radio so I don't know if it would work for you. Also the small free papers that you pay for the ad works well , usally fairly inexpensive.
Flyers to civic groups that have something to do with the speakers talk are good to.
You sound like you have a terrfic job. I worked in a home store that carried rustic cabin themes we had quite a few of the items from the Hudson bay store . I sure miss that job I was manager and did alot of the ads and sales decsions it was fun. Too bad my boss was not much of an accountant and lost it all to the bank and creditors.
Hope i helped some , things can be different in the 2 countries shame since we are so close and have the same ideals. Good Luck you'll have to post the speakers here as I travel alot lately maybe I could plan a business trip around getting to one. It would be fun and I could meet you.