Regardless of what it costs you to make a cake you can only charge what the market will bear. But to do so, you have to find your target customer, and when you do, you should know your costs. But you should charge as much as you can. If you don't, you negatively effect the market price which hurts everyone.
With the new cottage food laws, lots of ladies baking cakes are undercharging. If they have hopes of one day owning a storefront, they are shooting themselves in the foot by driving prices down.
If you simply decide a wage per hour that you want to make and add your costs to that, you become a cake making service, not a cake business. A cake business considers what it costs to pay employees to make a cake and then make a profit on top of that.
Your target market is not people who want to pay $40 for a grocery store cake. Nor is it people who want to have a cake lady who makes awesome cakes for really cheap. Nor is it a person who wants you to charge less because there will be lots of people at her party and, "surely it will drum up business for you".