I've been away from this forum for a while, but I will take a crack at this.

What to look for in a bonsai is a subjective question. Some people look for mature or "finished" trees, while others look almost exclusively for bargains, trees that are not pricey but have potential. For the first 8-9 years of my bonsai endeavors I have been in the latter category, seldom spending more than $50 for a tree but now that my tastes have matured and my skills have increased (however meager they still may be), I am spending more.

What I liked about this article is it shows what a world-class bonsai artist can accomplish over decades of work with simple nursery material. At the same time the take home point was that now with the benefit of experience he realizes that by spending more money, not necessarily thousands of dollars, but certainly more than $20-50 you might spend at a typical nursery, he could have done much better in much less time.

If you want some good examples of what to look for pick up "Bonsai Survival Manual" by Colin Lewis, some very good advice in there about what to look for in different species of trees out there. If you want more info let me know and I can share some of my notes.