Purchasing recently ran a feature article that describes Five Musts For Justifying IT Budgets. While a useful primer for those who have had problems convincing the business and IT to sign-off on procurement and technology investments in the past, the article completely misses the boat on how to really close-the-deal on getting budget for new projects. Sure, it's important to "understand how existing procedures affect purchasing, accounting and other departments" and to "quantify the impact of staying with the current system vs. moving to new software" but all that stuff should go without saying. In my experience, what really matters most when selling new technology internally is positioning the afterlife (i.e., how great will life be after pulling the investment trigger).
Indeed, if you can't succinctly articulate and sell the afterlife of a technology investment, then you'll come up short every time (on adoption and usage as well). Like missionaries who must sell their God to unbelievers, procurement and operations professionals must convert those pagans and atheists who insist on the old way. Sure, while a few crusades might be necessary on the journey, basic missionary skills -- not to mention a few good sermons -- will go a long way to win over many holdouts. So don't just build that financial model. Win over their hearts by helping them imagine how great life could be after the investment.