Grass roots marketing is always best (and cheapest). If you are near schools, "partner" with the schools and offer incentives for the school - for example, 15% of sales this Tuesday will go to John Smith Elementary, just come in and tell us you are with JSE. Get the school's buy-in and they will promote it for you. Provide them with stickers to give the kids that remind their parents.

Another great proven way is to employ college kids to promote your business in exchange for free food.

Also, Fiverr.com has a lot of VERY inexpensive options for local marketing.