The best advertising is word-of-mouth for the 18-35-year-olds. If at least one of their friends is attending, then you will boost attendance.
Where do you find a bunch of college friends? Go to the clubs. Some of those clubs are so close-knit that if you can convince one of them to go to your event, then you may have secured a good 15, 20, 30, or more to your event.
Find the closest campus to you and discover when certain clubs are meeting. Notice which clubs would most likely be your biggest fans and ask to sit in a meeting or two. Become a mentor of sorts.
While there, ask the members of who has a Facebook account. My guess is that at least 3/4 of them will. Get their names so you can invite them as friends. Through your own Facebook account, you can post events and even have people RSVP. Target those college students.
You can always put ads in campus newspapers or make a radio spot or any number of traditional methods, but connecting with clubs has shown me the most success.