I charge $7.75 base price for tiered cakes and $8.25 base price for topsy turvy cakes. For this one, I'd charge $9. HTH
Is that per serving?
Our base rate for multi-tier cakes is $5/serving, for that cake it would probably be around $8/serving.
Of course that doesn't really help you, since you need to first determine what your costs are, including ingredients, labor (based on an estimate of how long the cake will take * your hourly wage), and overhead. You also need to make sure it's legal in your state to sell cakes made in your home kitchen, if not you'll need to rent commercial space.
Sorry, yes, that's per serving.
Also are you planning on making it 3 tiers? A two tier cake would easily serve 25 (more in reality) because you would probably use a 6 inch top and a 9 or 10 inch bottom. If you add the 3rd tier they will have a ton of extra cake. That's fine if that's what they want but they pay for the servings of the cake...not the number of people at the party
Don't forget to include the pricing of your support structure. If this is your first topsy turvy you need to do a test run cake, even if it's just a smaller 2 tier. Topsy are tough. My first one completely crashed.
Tips of Topsy Turvy cakes:
No slippery fillings - only Buttercream or ganache between the layers
Use ganache under the fondant for a super stable cake
Get a really good support system...something like SPS is a good idea. There is enough pressure with the angles and the carve out that if your dowels are the least bit off you run a really big risk.
Good luck on your cake