Cost of supplies + labor + profit.
Most people on here base their price off the per serving. It is hard to say just looking at a picture what size the cake is and how many servings that cake makes.
Prices also vary around the states, so it is hard for anyone to tell you exactly what you need to charge. Their costs, overhead, experience may differ from yours.
Guessing that they used a 5x7 edible image on the cake, I'd guess that cake is an 8x8. It's difficult from the angle to determine if it's a 4" high cake or a 2" high cake, but to me it looks to be about 2" high. Based Wilton's party cake chart, which uses a 2x2x1.5" piece, that cake would serve 20. Being all buttercream I would probably charge $60 for the cake (I wouldn't bother adding anything for the booties) but I'd add on the cost for the inedible decoration in the corner and the cost for the edible image. In my area, it costs $10 to get the grocery to print out an 8x11 sheet, regardless of how many images I've managed to get onto that. So I'd probably charge $75-$80 for that cake myself. If you are making something bigger or smaller, you'd have to price it up or down obviously.
If you're making the same size 8" square cake but it's 4" high, then according to Wilton that cake serves 32 and I'd charge $95-$100 plus the cost of the image and the inedible decoration in the corner.