Here's how I made my own sidewall cutter.
I started with a piece of aluminum angle, filed and sanded smooth so it wouldn't scratch the ski base. I cut a piece of plexiglas for use as an edge guide, with a half-moon cut out of it to provide access for the cutting bit to reach the sidewall. As a cutter, I used a 1/8" lathe tool bit, held in a boring bar from my lathe. I attached the boring bar holder to the rest of the device with a C clamp.
It's not as convenient to adjust as a commercial one, but it's workable. To adjust the depth of cut, you loosen the setscrew in the end of the boring bar and slide the tool bit in or out. To adjust how close to the base edge of the ski you want to cut the sidewall, you loosen the C clamp a bit and slide the boring bar up or down in the holder. The holder has a slot cut down the length of it (you can't see it in the photo, it's on the back side) so that when you tighten the clamp, it grips the boring bar and prevents it from sliding or turning.
(To make a really nice one, I'd have to figure out a way to use micrometer screws for each of those adjustments. But I was too lazy and this seemed good enough for me.)
I tried it on a pair of junked "sacrificial" skis and it seems to work quite well. See the curl of sidewall that was cut off.
(In the picture below, the blue spring clamp is just there for the photo to keep the cutter from falling down.)
Ta-da! Almost as good as the SVST one, and I didn't have to spend $200