Let's break that down. You've got the cost of getting it to mars. You've got the cost of the rover itself. You've got the cost of operations.
Cost to mars is fundamentally about mass and size. The rover uses curiosity rover parts and is about 3 meters long, 2.7 meters wide, and 2.2 meters tall. Mass should be about 900 kg. They plan to use an Atlas V for launch which costs about $200m. Balance: $1.8 billion. But wait, this article says the LV cost 20% of $2.5b or $500m. That's quite a price range, but still leaves us a balance of $1.5 billion.
As mentioned, this rover uses parts made for the earlier curiosity rover. Basically it's curiosity 2. I can't find costs for it alone or for operational costs.
$1.5b should get us more than a radio control car that can barely do any exploring. What if we did the following instead...
A high school challenge: for $1000 each, high schools compete to build small rovers with a standard battery, camera and solar cell package provided to them with perhaps one other instrument of their choice.. SpaceX sends a quantity of them in it's 2018 red Dragon flight. The kids operated the rovers for free. Scientists get to look over their shoulders as much as they like. Expect each rover to have different methods of locomotion. Let the kids innovate and explore at their pace in whatever direction they like. Assume each rover is about 20 kg, they could send about a 100 of them per Dragon.
A hundred small rovers going in different directions would do a lot more exploring than one $1.5b rover and cost about $1.499 billion less.
My entry would be a regular radio controlled car inside a huge clear plastic ball. The weight of the car driving up the wall of the ball would move it in any direction. The ball would get scratches, but so what? Another method of locomotion might be jumping.
I suspect we could save money by electing these people...