Build the business case for budget
We generally use the wrong metrics to show the value of acquisition to management. Metrics like donors acquired and break-even duration don't tie back to short-term revenue or show the impact on long-term organizational health. We must change the way that we approach the business case to secure the funding necessary to keep the organization healthy.
This is a long-term investment — use long-term metrics. Measuring the "long-term value (LTV)" of the constituents acquired helps you show the value of the acquisition program over time to the organization as well as helps you make smarter decisions about how to pursue acquisition in the future. Measure the LTV at various intervals, including lifetime, and roll it up to both the list and the marketing effort. You may find, for example, faith-based lists convert less donors but are extremely profitable long term, or that certain catalog lists have a high acquisition count but negative LTV. Taking the long-term view may hurt short-term statistics, but remember the big-picture goal is long-term organizational health.