I need a wordpress web designers input – urgent

Hi there,
I’m part of a small e-commerce start-up. We’re using wordpress as our platform. We’ve hired a web developer who has been less than impressive to date.
Our website is a buy/sell platform where on one webpage users can create a ‘store’ (i.e. profile) that features their products for sale and a blur about the seller etc. On another page, is where users can search for products (Think Amazon.com for this part) and brows through or make a specific search for items.
It seems that the wordpress/plugin design layout isn’t quite right for what we want so were going to show our designer the custom design that we need.

My question is, how long could it take to change the design to what we want….and fyi, it currently is nothing what we want. Could someone provide a best case to worst case scenario in terms of time period to design these 2 pages properly?

Thanks for the help.