I have a client that wants to have dummy tiers in her wedding cake, and just have a 6 inch round on the top to cut for the wedding. I have never made a cake with dummy tiers and have no idea on how to even start to price them. Also if you have any tips on working with dummy tiers that would be greatly appreciated since I have never worked with them before.

charge almost as much or as much as for real cake -- it's all the work for sure right?

Exactly what -K8memphis said!  Dummies cost as much as real cake and require the same amount of decorating, so I charge the same amount per serving as for a real cake.  A lot of things are actually harder to do on a dummy because it is so light.  You will need to find a way to secure it to your turntable.

Here's a blog post I wrote about charging for dummy tiers.

https://cakepricer.com/how-do-you-price-dummy-cakes/