An 8" cake is about 14 PARTY sized servings. Most people dont cut birthday cake like they do wedding cake, and most bakers don't charge for birthday cake like wedding cake. Even on Earlene's chart, an 8" cake is only 15 wedding servings. I would price that cake at approximately $45 to $50 in the midwest which is about $3 - $4 a serving. Course in LA or NY, I'm sure it's a different story. If you have bakeries near you that offer similar cakes, go in with that picture and ask them for a quote. That's how you know what to charge in your area.