Hi Christine,
I apologize It took me this long to answer.
I would start by doing some research on different vendors and the different cost options. Pretty much you will need to find out who gives you the best interest rate (7%, 10% etc.) then draw your analisys from there. The "i"...
I would love to answer your question. What is it that you are avaluating or making the economic analysis. Can you be a little bit more especific?? the interest value varies accordinng to the options you have. Can you tell me more about what is it that you arer doing? Maybe I will be able to help...