Multi vendor website build

I want to start a website The crafters' Barn (we do have a current website but it's not appropriate for growing the site) where people can sell their handmade items for a small fixed monthly fee. I have bought software but have realised I don't have the skills to make it look as good as it needs to. It's open source PHP with CSS style sheets.

I would like quotes to either cusomise this software for me to make it look better and work sleeker, or to build a brand new website. i'd like quotes for both options if at all possible.

The end result needs to be similar in idea to Etsy.com or Folksy.co.uk The software I have which could be customised is iscripts.com Multi-cart. they do offer customisation but I want to liaise with someone in UK who will understand better the concept and how I need the design to work. I currently also have an linux based unlimited webhost package with webfusion to host the site on (the software is uploaded there at the moment). it takes too long to sort anything out with them with time differences etc,

The final site needs to be Multi-vendor, with all sellers being able to set their own P&P rates etc in whichever manner they choose (flat rate/weight bands etc) they need to be able to sign in and upload products for sale easily, with multiple photographs for each product, and a thumbnail for a front page or "sellers page" summary. Feedback needs to be able to be given from sellers, and they need to be able to receive all payments directly to their own paypal accounts. it needs to be able to accept unlimited numbers of sellers with unlimited products each, and with the possibility of product options (colour/size etc). it doesn't need to be multi-currency as payments will be paypal so they can all be accepted in sterling.

From my point of view it would be nice if the monthly fees from sellers to me could be automated. But that is not essential as I expect I could do it a different way.

If you could bid on both working from scratch (it might be easier) or working with me to customise the software i have that would be great. This might all be outside my budget but I can't do the business plan and know if it'll work without knowing the idea of cost. thanks for your time reading my post.