@DAB mentioned on my research post earlier in the series not to forget the costs of marketing, shipping and handling. These were not things I knew much about so I've done some more investigation. as I've been busy with the Enchanted Objects Design Challenge and Robox printer review these have just ended up as a list of useful links, I'll be expanding on this at a later date.
Marketing
https://medium.com/@BoltVC/hardware-by-the-numbers-part-3-logistics-marketing-1c7f37b64c05
http://blog.dragoninnovation.com/2014/12/16/dfm-course-12-costing/
A new web site for finding the cheapest PCB manufacturer[UID=f880]
Packaging
C5 C4 C6 Royal Mail Mini Large Letter Cardboard Postal Mailing Packing Boxes PiP | eBay
http://makingsociety.com/2013/06/how-to-package-a-product/
Fullfilment
Introducing Arachnid Labs new, faster shipping - Arachnid Labs
http://andrewminalto.com/fulfilment-houses-the-good-the-bad-the-ugly/
Fulfilment by Amazon: Features & Benefits - Amazon Services Europe
Is anyone else using a fulfillment house? - Tindie Community
Fulfillment Companies - Tindie Community
http://blog.tindie.com/2014/09/so-you-want-to-start-an-open-hardware-business/