If it's for a friend and you don't want to charge her much, figure out the cost of ingredients, and add on what you think is fair for your labor.
So it's maybe about 18 servings, first cake, not a bad job - how about going with the $2 per serving and charging $36?
Another way is cost of ingredients x 3 = price of cake.
Or as was said before, if it is a friend you could always figure out cost of ingredients and just charge that.
If it's for a good friend I wouldn't charge much either.. ingredients would be about it.. (I bake from scratch so that adds up quick).
Normally I would make sure to iron out the price BEFORE you bake the cake. It saves everyone grief. Because most people are used to the cost of Wal*Mart cakes. On a normal basis I would charge $4/serving for that cake and $15 for the bow. If it's 12x18x2 that's 50 servings so $215.00. I bet if you told your friend that she'd poop her pants right? This is why you work out the price first.. this way there are no surprises and she can can say no that's not in my budget BEFORE you bake and put your money into it. 
18 servings??? No way. Even if it is 12x12x2.. that's 35 servings.. a 12x12x4 serves 70. And it isn't square.. it's on (what looks like ot me) a sheetcake board, and if it's 12" one way it has to be 18" the other. I think that was a typo. A single layer 12x18x2 would serve 50+ 2x2x2 servings.
I was in a Walmart yesterday that had a bakery (my local one doesn't) and I had to laugh to myself - between the wedding cake display and the $7 "chocolate truffle* cake.....cheap cake isn't good and good cake isn't cheap.
I'm lucky if I only spend $7 on just the chocolate when I make my chocolate truffle cake.
HA!! No kidding Sue.. I just made a chocolate cake with chocolate mousse for filling and ganache as the icing.. and 8".. the thing cost me $30 to make.. most of which was spent on the chocolate (and I just use ghirardelli.. nothing special).
According to Wilton's party serving, a 12x12 - 2 layer cake should be about 48 servings. Without the 2nd layer that's 48 half servings. So in actuality the cake is really only 24 party sized servings.
With regards to the complexity, it's a fairly simple cake that should not have required that much time. Your cake is not totally covered in fondant.
I would suggest charging no more than $50 for your cake based on serving size and complexity.
It definitely depends on what chart you go by, because I go by close to the wedding chart and a 12x12x4 would serve 70 (72 according to Wilton) wedding servings so half would be 35. That's a 2x2x2 piece of cake.. pretty standard "sheetcake" serving. But all that aside.. if you LOOK at the cake in the picture.. it's a rectangle not a square.. either that or it's a a REALLY wonky picture, but it's on one of those show-n-serve type sheetcake boards.. so I'd be willing to bet money that it's not a square cake.. a 12x18x2" cake can be cut into 50 plus 2x2x2 pieces.
Its a square cake pan, I just checked. I got it as a set, wilton brand & it says square set. In the pic it looks funny cuz the site made me size it down, cuz it was too big to upload it on here. Also the cake board was one I got from hobby lobby, it was rectangle & too long so I cut it down to fit the cake better. Thanks everyone for ur thoughts
Ahh.. well the distortion definitley makes it look like a rectangle. Next time you need to downsize a picture go to resizemypicture.com
http://www.resizemypicture.com/resizer/resizer-main.php
they do it for you.
So if it's a 12x12x2 then it's 35 servings by my chart.. Being for a good friend.. I'd charge for just ingredients.. if she's a GOOD friend. If not then discount how you feel, but full price would be$4/serving or $155 from me. I wouldn't go less than $2/serving.. and that's pushing it. It's not cheap to make a cake.. especially if you bake from scratch.
I'd charge $45 to a good friend based on size, detail and cost to make.
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