Consider your own home. If you have a finished basement, starting a preschool in your own home is the least expensive option of all. Lori Ferguson, of Parker, Colorado, started "Sunshine Preschool" in her basement. After several years, she expanded to a commercial site, and as of 2010 employs over 10 staff. You'll need a home daycare license and additional homeowner's insurance. In addition to very low overhead, you'll also enjoy the advantages of a large tax write-off.
Contact local churches. Church preschools have a built-in student base, drawing from the families within the congregation. Before you approach a pastor, do your research. Talk with preschool directors from other church preschools about the logistics of running a preschool out of a church. Find out what the benefits are for the church, so you can present a persuasive proposal. Church preschools often qualify for a religious exemption from licensing laws that can significantly reduce costs.
Research private schools in the area. If a school doesn't have a preschool, approach the school board about starting one. Have a well-researched plan, detailing projected costs. Write a proposed mission statement and curriculum that supports the philosophy of the school. A major benefit for private schools in opening a preschool is that the preschool children often continue their education at the school, boosting enrollment.