Is there an easier way of getting estimates from development without a full functional spec document? Our dev team has serious commitment phobia!

Introduce your dev team to the point system – story points (agile) or function points (waterfall). To get your baseline, take a recent project or two and count the number of user functions that were delivered. Each one is worth one point. Total the points and divide them into the total number of person hours for the project. The result tells you the number of development hours it takes to deliver each point – your development productivity factor. For your next project, estimate the number of user functions based on the business or user requirements and multiply it by your development productivity factor. Your estimate will be comfortably in the ballpark.