http://www.janes.com/article/46129/pentagon-finalises-f-35-l... "The US buy is for 19 F-35A conventional take-off and landing aircraft at USD94.8 million apiece; 6 F-35B short take-off and landing aircraft for USD102 million each."
That does not include an F-135 engine for each jet, which is anywhere from $10 to $15 million depending on the variant.
So while the F-35 is more expensive than the F-18, I do not believe the figures bear your "3x or more" assertion.
Also it's difficult to compare the operating costs of a fully mature aircraft like the F-18 with the F-35, which is still being tested and developed. I don't think that is an apples/apples comparison.
Disclaimer: all opinions my own, not those of my employer, etc.
http://en.wikipedia.org/wiki/Lockheed_Martin_F-35_Lightning_...