"My intent in collecting is to acquire trees for free"
Um, but they're NOT free


. They require work to get and know-how to get them to survive--even if they're only seedlings. This knowledge takes some time to acquire and refine. The trees you dig now will probably die. That's the way the learning curve works. Oh, by the way, forget the "collecting" advice you read in books--it's mostly La-La land advice. Things NEVER work that way in the field. "Spading around" a tree is a very inefficient way to prepare a tree for next year's collection.
Additionally, the equipment, time and resources you use are your payment for whatever you dig--not only with sweat, bug (or worse) bites, destroyed knuckles and knees, proper collecting tools (shovels are mostly unnecessary in digging hornbeam, but hand pruning saws, sharpshooter digging tools, hand pruners and trowels are invaluable), soil components (no, you can't plant a collected tree in a pot with soil you dig along with it) and shelter (winter protection is a must for newly dug trees in their first year in a container), etc. all add to the costs. They're one time up front expenses (until the tools wear out--which can happen every season with pruning saws), but they are expenses.
If you're only after seedlings-you're probably better off just buying them. It would be cheaper and more efficient.