I would like to know what all the non professionals charge on a half sheet cake with a 3d ducky with fondant. This is the 2nd set of cakes for her parties I have done and I have no idea how to charge her. By no means are my cakes professional but I think there ok. I would just like some oppinions on how to deal with this. Thank You.

If you aren't doing this for a living, more as a paid hobby, you might consider adding up all of your costs and then multiplying by 2 or 3, depending on how much you think your time is worth.

If you are planning on making this thing more of a paying job, you need to survey the bakeries in town and see what their per serving price is, then park yourself in that ballpark.

karateka's advise it right on.
My personal opinion would be:
Is the duck also cake or all fondant? Makes a differece.
A sheet cake 12x18x2 should sell for about $40; For a cake 3-d duck covered in fondant add another $30. If the duck is fondant only then I'd say about $10 so a total of $50 there or $70 if it's cake.