I don't think they are as expensive as one would think. Like I posted a week or so ago, I think they can be made for around $20k. I think that could be what RAD pays for them. That's cheaper than a new car these days. As lara likes to point out, it looks like a lawnmower. Well, here's a robotic lawnmower for $3500:
That leaves $16,500 to upsize a bit and add cameras, sensors, and the AI for roving security applications.
Here's my breakdown using a golf cart as the basis. Obviously many of these parts are not actually in the RADbot, but they are representative of the components I would expect to find in them, IMO. These are also full retail prices. Note the golf cart cost is adjusted down because while being a similar device in that it is a four wheeled electric vehicle, golf carts are about 1000 lbs and the RADbot is only about 250 to 330 lbs. I reduced the price of the golf cart by 50%.