Good question. Radio and tv stations are required to do Public Service Announcements (PSAs) free of charge. You might contact as many as you can with info about the event in the form of a press release. What is your demographic in Gulfport and the surrounding area? If you want to appeal to a certain age group, then choose a station that plays to that audience. If you want to make some "noise" with a lot of high energy, then consider a rock station. It's tough because you don't want to turn anyone off either. You could also go with an all news station. Some of them partner with tv stations and you get twice the bang for the buck (still free). But music could be nice. A jazz station is a good in between. There may even be a local high school jazz band that could play. You should not be charged for these things. It's all about community support and co-promotion.

Good luck with your event!