[FUNd]

The responses here prove that there is no one accepted method of calculating or presenting the cost of a MCA. Many of the answers deal with the marketing aspect of the business, not the analytical.
Let me restate the question. Without trying to wiggle out of an answer what do you tell your client if they flat out ask what the interest rate is?
Bob

I answer their question with a question. Interest rate? What interest rate did your local bank offer you? Oh, that's right, they didn't, because you're a deadbeat POS with a 599 FICO and a business that is barely hanging on.