GroupDeal - e-commerce system for collective buying model

We are looking for an automated e-commerce system which can allow us to sell vouchers based on a collective buying model. The voucher entitles the holder to receive a product/service at a discounted value (the deal). To receive this deal, a minimum number of vouchers must be sold (the group aspect of the deal). Users will have a certain number of days (i.e. 3 days) to sign up for the voucher, before the deal is complete and we move onto another voucher. At any given time, we will be offering only one voucher at a time. (although the system should be able to support multiple concurrent deals if needed) If we sell at least a minimum number of vouchers, and not more then the maximum number, then all the users who signed up for the voucher will be charged for the purchase and have the voucher sent to them via email. There will be multiple discount levels based on the number of users who sign up. So for instance if at least 10 people sign up than they will all receive a 30% discount, if 30 people sign up they will all receive a 40% discount, if 50 or more sign up they will all receive a 50% discount. If the minimum number is not met, no one will receive the voucher and no one will be charged for it. When a user signs up for a voucher, they will enter their payment information and agree to purchase the voucher at the end of the deal given that the minimum number is met. Please see [login to view URL], [login to view URL], or www.groupon.com. Note that each of these sites works off a deal-a-day approach, while we plan to offer a deal that runs for a administrator set number of days. (i.e. 3) The solution will need to: a) Allow administrator to create new deals (voucher/product) and specify an end date/time, minimum order number, maximum order number, and discount levels. b) Facilitate payment options including paypal, google checkout, and direct credit card transactions through paypal pro. (No payment information should be stored on our servers!) c) Store authorizations for customer orders to be processed (captured) in batch based on the expiration of the end date/time and whether the number of orders has exceeded the minimum order number and not exceeded the maximum. d) Allow customer accounts including login to save purchase information for later use (i.e. billing address, order history, etc.) e) Upon processing the payments in batch the system will add orders to customer account and send out emails to customers informing them of purchase completion. f) Customers will need to be able to login and download templated vouchers which will contain their name and a uniquely generated security code, and appropriate discount based on discount level reached. g) A list of the completed orders will need to be generated by voucher/product and sorted by customer last name and will include security code. A detailed set of requirements has been attached to this post. Please note that our preference is to use established products, i.e. wordpress / joomla / drupal for content management, oscommerce / wp e-Commerce / wp eShop for user/order management. The main bulk of the effort will be in facilitating the batch order processing and voucher distribution/management NOT in installing/configuring the application toolset. As such we will expect a detailed explanation of your proposed toolset and how you will approach fulfilling the requirements. You can see the website: [login to view URL] as a good example of what we are looking to accomplish with the addition of the discount levels. Note that this website uses a custom flash payment system to process their payments, whereas we are looking to use/integrate a trusted third party service (paypal/google checkout) to manage our payment management.