Full website design with individual account log ins for customers

I require someone to design a website which will allow clients to have their own admin areas and to upload their own images or items for sale. it will also need paypal link added, to allow areas to upload comments and also articles to be added.

There will be an ongoing requirement for support, for SEO and genaeral assistance in monitising the site where possible.

An NDA will be required to be signed but an initial indication of the website cost ir required, anyone that has designed a highly functional and interactive site such as this would be desirable.