Step number one, buy in bulk! Many online tree nurseries will give substantial discounts for trees purchased in bulk. An apple tree might cost you $30 or more but when you go to buy 5 or 10 they can drop our price point significantly to $20 or I've gotten some as low as $10. Depending on the retailer you might even get better pricing. These bulk discounts usually only apply to the same variety tree meaning you will likely have to buy 10 of those Gala apple trees to get that discount.
Step number two is to visit your state's nursery. If your wallet isn't ready to buy your trees in bulk you can always check out your state's nursery. Chances are you have an in state or nearby state run nursery that grows seedling stock to sell to local landowners. They will often sell native trees that fall into a few catorgies: aesthetics, forest products, soil protection, watershed protection, wildlife habitat, and windbreaks.
Great deals can be had if you know where and when to look. As far as the state nurseries go you can usually get the best availabitiy in the late fall or early spring. I have found trees like American Persimmon, Paw Paw, walnut, oak and black locust for as cheap as 100 seedlings for $40.00. Check your local state nursery and sale on mass plantings today!
Your third option is to plant your trees from seeds The next easy way to get cheap trees is to save seeds or buy seeds. Growing trees from seed can be a great way to grow large quantities of trees in a very inexpensive way. Just think, every time you eat an apple save the seed, stratify it in your fridge for the winter and plant it out come spring. Find a local acorn or walnut tree. Gather all the nuts you can find and plant them out. Yes it is a bit more complicated than that but how do you think most trees reproduce in nature? A seed is usually eaten, stored or forgotten, and buried and it sprouts and replicates.
Finally using cuttings for your tree propagation can be very inexpensive. Some plants and trees grow great from cuttings. This is a cheap and easy way as long as you have tree stock available to take cuttings from. Cuttings can be as simple as taking your summer or winter prunings from existing trees, adding some rooting horome, and planting them out. What works best depends on what plant you are taking cuttings from but a lot of trees and plants can be rooted using cuttings.
If you want to expand your plantings going forward try one or all of these methods and you will find yourself swimming in trees in no time. Please feel free to post any comments and suggestions for any cheap tree sources you might know of.