One of the cheapest ways to buy trees and bushes is to order from the Missouri Department of Conservation Department. Prices run from $.16 to $.80 per seedling. You can start ordering on November 1st.
While the prices are inexpensive, most times you have to buy ten to twenty-five at a time. This would be a great project for a garden club or get together with your neighbors and share a bundle of trees/bushes.
The pictured tree is a Tulip Poplar which is a host plant for the Tiger Swallowtail.
Here are some links: