Hello,
Here is my brief, but hopefully helpful advice: funding (unless you are up for fellowships) represents a symbiotic relationship between the student and the department. You could stress how crucial funding is for you and how it is a determining factor as to whether or not you will pursue your studies. Another way to tackle this is to focus on the potential assistantship that you may have at that university. What is the school going to get from you? (either as a TA, instructor, RA, etc.) Why should they give you funding, What strengths do you have that others may not, etc...
I am not sure if that helps, but good luck!