Gosh its hard to tell without seeing a pic of the cake or knowing what you are makeing it for or how much you usually price things but for me a simple cake no fillling no fondant I would say 30 but then agian I tend to under price.
I just did a cake that sounds exactly like this, it was a plain sheetcake the same size, with borders and a FBCT of the Steelers logo and "Happy Birthday" message on it (no pics uploaded yet). The Columbus City Limits are literally right across the street from me, and I sold it for 60 dollars, that's including 10 dollars delivery to Hilliard. The lady said she was getting a great deal and didn't bat an eyelash at the price I quoted her. 
Hope that helps!
Diana
I charge $45-50 for a 12x18, single layer, buttercream. I do use a box mix though, so give that some thought. And I usually charge $35 for an 11x15.
A lot of people have scolded me about my prices, so I am just beginning to feel comfortable charging these prices.
I do vary them though. If it is a really simple design, then I tend to charge the lower price.
In my experience, most people (not all) tend to give a tip as well.
Good luck,
Bethany
I know my area is way below most of you, and you would probably feel insulted if you had to charge what I do. I am also trying to build a business and purposely have my prices a bit low, even for our area. For a 12 x 18, boxed mix doctored up, plain buttercream, no fillings, no frills, I charge $22. It goes up from there if they want to start making extra requests. I know the bakery in town is $28 for the same thing, and a lady in my neighborhood who has been doing cakes for about 40 years would charge $26. So I'm probably not much help to you.
Everyone, count yourselves lucky that people realize what you're worth. People have told me I'm too high on some things. 
I tell them to go to Walmart. 
I use a very doctored box mix for mine as well.
Thanks, guys! You're awesome! This is for my best friend, but I didn't want to figure that in, and I knew I couldn't really do it without bias. I spent $20 on ingredients today at the store just for the cake (minus about $5 for the things from that I won't use - extra shortening, butter, etc). I was thinking around fifty dollars. This is kind of what I'm going to do (stolen from someone in the gallery); we decided against the FBCT. It's for a party for her daughter's adoption finalization on Saturday.
Thanks again!!
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