You've missed quite a lot if you think all those maples are are just trunk chopped nursery trees. They're not and while the prices are juuuust a bit high, I think they're pretty good for what they are.
For instance, this straight trunked chopped air layer has an exceptional nebari. Better than ANY I've seen in a nursery grown tree. The person that air layered knew WTF they were doing. They got even roots all around the trunk and knew how to thin them out to get a flat even flow of roots in 360 degrees--which as anyone who has air layered a tree knows, is a challenge.
Getting the nebari right is almost 80-90 percent of making a tree. It is that important. Branches come later and aren't all that hard to get set. Most anything you do with this tree from now on will likely be successful because of that nebari.
You can get lower priced materials from places like Driftwood Bonsai and big box stores, but you get what you pay for. I took a spin through
Diftwoods site, has nice material, but not comparable. Roots and nebari on most of what I saw range from meh to a mess...You will spend five to ten years sorting some of that out, depending on species and individual tree.