My claim is that the pictures themselves are probably only worth $100k or so, and you can read the comment again to see how that tracks semantically. The experiments, maybe ten million unless they can demonstrate that they have some sort of value.

A "viable billion dollar mission" includes all sorts of other things that are of value, including developing capabilities to do things that are strategically important, which I would claim is where a large majority of that billion dollars comes from. Similarly, I would expect that JPL would very much inflate the value of their own work. Everyone does.

Also, I see "incapable of being measured" with "broadly : indefinitely extensive" tacked on in the MW definition. There is no requirement there that "immeasurable" mean "large", just "incapable of being measured" with the expectation that it is used when describing things that are extreme. My most recent use of "immeasurable" was "immeasurably small" which I'm sure you would agree is a proper use.