This application doesn't necessarily require an expensive pulsed laser to do the job. I've performed rust removal using both a basic college 50W and an 80W CO2 laser engraving machine. But this is just using a convex lens to create a small high energy point and moving backwards and forwards. The cost factor comes down to how effectively the job can be carried out and how expensive the technology is to allow it. Laser rust removal devices use a cylindrical lens to create a tightly focused line. This eliminates the need for scanning and quickens the ability to affect a larger area. If using a cylidrical lens, you are better off with a fibre laser due to the shorter wavelength (higher beam intensity than CO2) which is more costly. To go one step further would be to use a pulsed laser as this would deliver the energy needed without needing too much average power. But with all these additional advances, it stacks up as cost. But undoubtedly what you are mostly paying for is the r&d and profits desired by the manufacturer. $500,000 is excessive IMO. I've seen backpack solutions before that cost far less.
As for safety, you are using a Class IV at the IR part of the spectrum. Obviously there is a major safety aspect to consider. IIRC, I've seen systems that deliberately use a wavelength that doesn't harm the user if their hand gets exposed to the beam. But eye safety is paramount to the user and those around the device.
). They're typically Q-switch YAG/Fiber lasers at 10s to 100s of watts average output power with peak powers well into the 100s or 1,000s of kW. Designing and building something like that, and doing it well, is not cheap.