A small budget doesn't mean you will have no reachability. There are a number of ways you could do promotions now and into the future.
You may wish to network with local radio stations and begin relationships with them letting them know you are somehow serving the community. Figure out an angle for your story and make it positive for the community so that people will want to get behind your cause. Make sure your talent spreads the word to their networks. Word-of-mouth always helps. You never know what will happen or who will hear about it.
Consider writing a press release about the talent show. It costs nothing, and, if done properly, can get you noticed. These take a little bit of thinking and hardly any time to write up. If you have a really creative friend, ask him or her to help as well.
When you go out to promote the show, or any show for that matter, see who else in the area may want to affiliate with your show. Look at who's coming to your show, then start talking to local businesses to secure sponsorships. That will help with the cost of doing other types of marketing. There are other businesses that will support you if you show them that you have access to their market and can get their brand in front of that audience. I have a friend that does business-training seminars and his group gets sponsorships with companies such as Staples, and software companies. You can do it on a much smaller scale and be successful.
The goal is to get your expenses covered for the marketing expenses you may incur. The rest of it is word-of-mouth via friends associates and the networks of those coming to the show.