...for defects. But the cost to fix a defect tends to be lower when a project team has been proactive in trying to find defectsearly. And the overall number of defects is lower, lowering your total cost to fix defects for a particular release...
http://www.jrothman.com/Papers/are-we-there-yet.html
...organization and the business at large. Conversely, significant savings can be realized by identifying and eliminating defectsearly in the lifecycle, or by not introducing them at all. Gartner estimates the cost of fixing a security vulnerability...
http://www.findwhitepapers.com/whitepaper2199/