Walk into your local newspaper or radio station and tell them that you are a local author. You will probably get an interview or book review, and that is free publicity.
Leave copies of your book on consignment with any shop which will take them. Think outside the square. In addition to bookshops and newsagencies, try the local tourist information centre, knick-knack shops in small towns on the highway, any place where people are likely to wander around with some time and money to spare.
Leave posters advertising your book at the local library, cafes, bulletin boards.
Donate a copy to your local library. Leave free copies at your local cafe, with contact details inside.
Tell all your friends and relations about your book. Those who can afford it will be happy to buy a copy to show their support.