I'm not sure how you can sell them on DevOps in particular, but there's an entire category of 'best practices' where the cost for prevention is way smaller than the cost of even a single mistake. I think DevOps is one of those things. Don't look at it in terms of saving time or money, but rather insurance against much more expensive liabilities. Part of DevOps is "risk reduction" as well, and things like 'liability', 'reducing risk' speak to executives and business owners because they understand their own numbers, even if they don't understand how you'll be reducing that risk.