It's a complicated formula really. I have, however, streamlined it by using the UN model. Freepmail me with how much money you have and I will send you a bill for your credits. You may use them as soon as your check clears.
Dear Colorado Doug,
Thank you so very much for your generous offer. To make things quicker and easier, I will be sending a money order for $10,000. Please send the excess back to me as soon as possible. (etc.) :-)