I am having a major issue with pricing for this cake a client asked me info on...obviously because I am a bit intimidated of it and not sure if I need to be! If the link doesnt bring you right to it, It is the starry night by van gogh in the thumbnails. It will be for a sweet 16 not a topsy turvy just tiered plus the bottom tier will not be as detailed. She doesn't care if it is fondant or bc. Servings 90. Thanks
http://www.colettescakes.com/birthday_cc.html#

Estimate your cost (including ingredients, labor, and the overhead allocated to the order) and add 20-30% for your profit margin.

I'm not seeing how this cake could be done in buttercream, unless you are a true master with that medium. It is completely painted from top to bottom. I would be at $10 per serving for this cake, in fondant, and even that might be too low.

Here is one done in buttercream - looks quite involved to me. http://www.polyvore.com/sweet_literally_van_gogh_starry/thing?id=20519512

The buttercream one looks very different than the painted fondant. You need to clarify with your customer which look she wants, and also examine your own skills and determine if you are able to execute whichever medium she chooses. This is not a commentary on your skills, I'm not calling you out, but those are advanced cakes and I myself might be nervous about taking on this order.

ETA: I know you said the customer doesn't care whether it's fondant or buttercream, but the customer probably has no idea how different the two look. If she's expecting the Colette painted fondant cake and you show up with a deeply textured buttercream cake like the one in that link , she'll likely be disappointed.