Why is the robot tank chassis so expensive?

WHY IS THE ROBOT TANK CHASSIS SO EXPENSIVE?

I am a college student. We learned to use a single-chip robot. I have been searching online for a long time and wanted to find a cheap tank chassis, but I have not found it. It’s so expensive, why is the robot tank chassis so expensive?
After my in-depth research, I found out that there are some reasons for this.
The first, metal tank chassis was produced one by one with CNC machines. Without the production of abrasive tools, the production costs were very high.
Second, this is a very niche area. If you talk to someone about this thing, most people may not know what it is. Because of the niche, the sales volume is low, because the sales volume is low, so the output is low, and because the output is low, the grinding tool cannot be used, so the cost is high.
For the above two reasons, the robot tank chassis is more expensive.