Would suggest you read Plant Production in containers and/ or production of landscape plants II in the field both by Carl E. Whitcomb... he was my professor & both books are the authority on this subject.

What kind of trees are you wanting to plant?

I am buying land in Wisconsin and have found that several counties have tree sales, you can get bundles of seedlings (like 25) for $25. Also, our Wisconsin Department of Natural Resourses (DNR) has its own huge nurseries and you can buy 1000 seedlings for like $400. I don't know what state you are in, but google on tree sales in your state. Also, if your state has MFL (managed forest land) agreements you may want to sign into it, you get great discounts on taxes, and our DNR pays half the cost to tree it up.