We are planning a 40th anniversary party for my in-laws. My sister who has baked alot of cakes before is going to make the cake. I want about a 4 tier cake with buttercream type icing and just like straight line marks made with the icing knife, so not real difficult she says. We want 100 servings. She's having a hard time coming up with a price of what she should charge me. What do you think would be a good price? She has no relation to the people of the party but of course she doesn't want to charge me an arm and a leg either.