I would charge at least $100 for that cake as an 8" Round. Friends and Family can be a real pain in the rear for some cakers. Fortunately I don’t have these issues. To solve the problem once and for all you need to set very clear rules for them before they take advantage of you and you feel resentful. I agree with the others add up every single expense even water, dish soap, gas for the car as you pick up all the supplies, then add in all the hours you worked on the cake and details, pay yourself an hourly wage. Add it all up and you will have your price. Adding up everything x 3 works too, only if you are happy with end number. This works best for super simple cakes, but not cakes with many hours of detail work.
Teri, Ontario, Canada http://www.TeriLovesCake.ca