In terms of how much technology costs, you're right, it is insanely expensive. But I have some academic background on this subject, and it seems to me that one of the problems is that these new technologies (in terms of scans, etc) are developed by engineers at private companies, who then have no incentive to make those machines affordable to hospitals. The hospitals have to fork out millions of dollars, and need the machines in order to say they have the latest technologies so they can attract more patients, but as a result have to charge the patients/insurance companies more to afford those machines. It's a giant catch-22. It'd be nice if there were some governmental (tax, etc) incentives to make these technologies more affordable; however in today's pro-big business political climate, that doesn't seem likely to happen. For the people who make the decisions (and get damn cheap health insurance thru the gov't), there is no incentive to change. It's sad.
And in terms of preventative care...it is *absolutely* cheaper to have the diagnostic tests and preventative care. It is cheaper to give somebody $20 per month birth control then to pay for all the prenatal, delivery and infant care for a newborn. In addition, a mammogram, colonoscopy, etc is far cheaper than the surgeries, chemo etc needed to treat advanced stages of cancer. In addition, in purely economic terms, the more preventative medicine, the longer you keep people alive, and the longer you keep people alive, the longer they will continue to consume health care. So it's financially advantageous both short and long term.