I am making a birthday cake for the husband of someone I work with. She wants a 13x9 chocolate cake with vanilla frosting. Her husband is an architect so, on sugar sheets, I am going to draw in black edible pen the floor plan of one of his buildings. I figure 2 hours of labor and I have no idea what I should charge. Any help would be greatly appreciated!
Assuming 3 hours of labor (add prep and cleanup), a wage of $15/hour, market rate for your kitchen space at $15/hour, $20 in ingredients, and $10 in allocated overhead, you are looking at a cost of ($15 + $15) * 3 + $20 + $10 = $120 and a price ranging from $130-160 depending on your local market.
In my area a 13x9 would run at most $30. But that is my area. I've been to Chicago bakeries and double layer 1/2 sheets don't cost $100. So I think if you are doing this as a favor, charge for your ingredients and maybe something for your time. Or if it's for a party your invited to maybe make it your gift? I gift a lot of cakes. It helps me try things and I don;t have to search for something they are never going to use. And they can't return it 
Just for supplies alone, not counting a wage for yourself but including boards, covering, box, *ALL* supplies how much will you invest in this cake?
I've been retired for some 5 yrs now so I dont know what supplies are running. It also depends on where you are located. I think $30 is much too cheap - at least $50-60 is the minimumn you should consider chargine....but Jason's suggestion is way too high.. JMHO
Adjusting assumptions downward for a low COL area with a $10 wage, $10/hr market value, and $15 in ingredients, you would have a cost and price of $85 and $95-$110 for 3 hours of labor, or $65 and $75-$85 for 2 hours of labor.
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