Chopping up an $18 cypress requires no top skill. It simply requires the understanding that an $18 tree is an $18 tree and the room on the bench to keep it. You may, or may not, find a hackberry, or an elm, with trunk as substantial as this for $18...
Chopping is not what I've meant.
Over the years, I noticed that I learn the most from my experience when I can keep my tree strong and healthy, apply bonsai techniques (pruning, wiring, carving, etc), notice how the tree responds, and then try to improve my techniques and re-apply them....until the tree is nearly finished.
But this only works if the same tree is strong and healthy at all times. From the day you bought it at the nursery, until the day you consider it "finished".
The problem with these more-difficult species (more difficult for a beginner, of course), is that the student tries to do too much in a short time, and the tree slowly loses its vigor and health. It responds less and less to bonsai techniques (because the growth slows down), and at the end, even the correctly done techniques don't work anymore. Nothing can be more confusing than this, for a beginner.
This has nothing to do with dollars, $18, or $100, or $5. It is about working with forgiving species, that respond well to bonsai training.
I remember buying a large variety of species in my first years (Cypress, fir, redwood, and others), styled them into "instant bonsai", planted them into bonsai pots, and was tremendously proud of myself, spending ours admiring my masterpieces. I felt like Mr. Myagi, only younger and better-looking. Of course, nothing survived over a couple of years, simply because they couldn't take agressive pruning, constant tampering, and putting them into bonsai pots way too early. Plus, with species that do not backbud from old wood (Hinoki, etc), I had no idea how to creat foliage pads. I just cut them back like an elm or juniper, and the branches slowly died, even on a healty plant. Not the best way to learn bonsai from those.
However, if one has good knowledge of the species, how much damage they can take without losing vigor, how to overcome the backbudding problems, how sensitive the roots are to root-pruning, etc., then it is like a walk in the park.
One has to remember that the biggest cost with a bonsai is not the money that you paid when you purchased the material. It is the time and work spent on them, in the subsequent years. To put all this into monetary terms (so that you can properly put into perspective the importance of the initial price), let's say that you pay $18 on a nursery stock, but the value of the time and work that you put into the tree in the subsequent 5 years is $5,000 (one hour per week, and let's say that you value your work at $20/hr). Not counting any other cost (water, fertilizer, wire, tools).
Why do you even care whether or not you pay $18, or $25, or $1, if this is less than one percent of the total cost that you put into it. So, remember that your time is the biggest cost of all, and it is irreplaceable. It doesn't matter whether you pay $15 or you get it for free, because you will spend the rest of your life working on it...unless of course you are a business, and hope for a quick and profitable turn-around.