Online store with extra features

Hi All, Thanks for reading. I need a simple script to create an online store with PayPal gateway, but not just a standard one... The store outlook should be like the normal one, but I don't want to have set prices for products (only guide price - e.g. RPP - may be displayed in product description). I need end users to be able to make offers for available products (anything to their own discretion - no reserve) until certain deadline is reached (customisable for every product). To make an offer user needs to purchase a package of credits / tokens / whatever you call it (preferably using PayPal - e.g. 10credits for $1.99 - packages customisable in admin panel)... Every offer they make for products in store needs to decuct x volumes of their credits - mechanism similar to "penny auctions". End users cannot see offers from other users, but need to have an indication where their offer currently is - e.g. your offer $10.50 is in TOP5 / TOP25 / TOP50 / etc. of XXX offers (need this also to be customisable - sometimes it will be TOP5/15/25, in other scenario TOP10/20/50 etc.)... End user can then increase an offer at any time (but cannot decrease it). Each additional offer also deducts the credit from their account. Once the deadline for the sale has passed top 10 offers made for the product are displayed and available to all users. I am planning to sell several items per event - e.g. 5 units are available at once, so I need the 5 top out of XXX offers to be accepted for payment and highlighted on the list of top 10 offers (this also needs to be customisable, as sometimes it will be 2,3 or 5 units). If there are 2 offers from the same user, which qualify for the purchase - the lower ones needs to be discounted and the next offer from the list will jump up. End users, who offered top prices then will be sent to the payment gateway to pay the price they offered - shipment details should be taken from the integrated PayPal account. On a separate page I would like to have the list of last week's sales with top 10 offers mentioned above available. I need few tabs on the top - e.g. Home, About, How it works, Current Sales, Last Week's Sales, etc. I also need a fully customisable admin panel with standard features: add / remove / change categories, products and their descriptions / images / etc, set credit prices for offers individually, add / remove / change paypal account, add / remove / suspend users, manually add / remove credits to / from user accounts in case of any promotions, disputes or refunds, create and send newsletter and maybe reminder emails / SMS, etc. I hope I haven't complicated the above too much. It's not that difficult as it may look like :) More details to be discussed individually with interested freelancers. Thanks.