You need several dozen engineerrs, scientists, two floors of office buildings at JPL, servers, technicians, testing facilities to maintain, and then there's the DSN time etc.

Given that, in terms of actual cost, a person typically costs twice their salary (once you've given them a desk, air-con, training, a pc, etc etc). Then consider that senior engineers are a $100k salary - that's $200k. $20M isn't a lot of good engineers and scientists. They're already saving a lot of money compared to the operating costs of the initial 90 days and the first few months after it. They're down to pretty much the floor of what it costs to operate them.

Given that they cost $800M to build and launch with a promise of 90 days ( $4.4m per rover per day ) - $20m year ( < $28k/rover/day ) is remarkably good value. And don't forget Mars Odyssey here - THEMIS and GRS have done some awesome science (they told us where to send Phoenix) - and could continue to do so if they found the money for it.


Doug