Bid button/system for Zen cart

I need custom design bidding / "request a better price" system for Zen cart. User will have request for better price button along with Buy Now. once user clicks on Request for better price, he will get input box to input desired value and click go. new price allow input price to be more than 65%, up to 100% of product price. If user inputs less than 65% OR more than 100% of original price, he can again request for better price. Once user has requested better price, and system confirms that, user will not be able to modify its price, and even if user tries to purchase it again using buy now button, that requested price will be final price for that The new price that user has opted for, will be displayed along with product, so that user will know at what price he has purchased it, and this is new price for his reference. So once system accepts the price that becomes final for that user, and in that case request for better price button disappears from that product. when product is added new modified [requested better price], gets listed in checkout list , and user can do checkout on those products This all process doesn't update actual prices in database so all different user who will login to website initially see original prices and then could request for better price over original price. Checkout and Shopping cart has been completely modified to calculate the new total prices, and user will pay according to new prices.