Are there less invasive and less expensive options for preventative screening colonoscopies?

Yes. Double contrast barium enema xray or ct colonography however if some thing is found on either of the above, you will still need a colonoscopy. If either are negative, there is no guarantee that something wasn't missed due to the prep or performance of those studies. Colonoscopy is the gold standard.
Not really, not yet. A colonoscopy is the best way to look for colon cancer because a doctor can get a very clear picture of the colors, shapes, and textures inside the colon (large intestine). Wherever he sees something suspicious, he can do a biopsy or cut out polyps. A little camera in a capsule isn't controllable and can't do biopsies. A ct scan can't do biopsies and isn't a direct view of the inside surface.