Website to preorder items with some parameters.

Hi all, *** The Website / Store *** I need a website or webshop were you can preorder necklaces, with a couple of variables lengths, carats, maybe diameter. As a customer you can choose how many carats you want, what the length need to be and maybe the diameter. The customer can place the item with the right settings to it's shopping cart. For each item there must be options. - Number of carats (14k or 18k) - Length (40 cm, 42 cm (standard size), 45 cm, 48 cm, 50 cm) The websites needs to calculate the price of the item accourding to this formule: Total price = (v+(f*k*g*(l/42)) where: v = fixed costs in euro, given / hardcoded. f = actual gold price (I already have this actual gold price in a PHP variable.) k = Number of carats (14k = 0,585, 18k = 0,750) l = length of the item, compared to the standard length. g = Number of grams of a item, given / hardcoded. I have a script that loads the actual gold price in a PHP variable, I will give you that so you don't have to make that again. *** Check-out & some backend options *** For the check-out, it only needs to send an email to the admin with: "New pre-order" and the items + prices. New customers have enter their details, where returning users can enter their ID + a password or something to The admin uses an other program to create invoices, and manage his customers, all the customers already have an customerID. Note: There are already 243 customers in that system (starting on ID 100) So on some way I want to set a customerID for the customer. I think this is the best way to do it: When the new systems goes online, all customers have to register again. Thewebsite automaticly set CustomerID to 344 (auto increment). The admin checks if the customer is existing, and edit his CustomerID to his customerID in the existing system or leaves it to the value when it's a new customer. In this way you don't have to do all the data entery of the existing system. *** Last notes *** It does not matter if you use a open-source ECommerce store and edit it to what I need or build a custom-build website. It needs to work. That is the most important part. There is already a Wordpress website + theme installed, you either can use that or make some new design or let me build in the custom code in to the Wordpress theme. If you have any questions, please, please ask them! When placing a bid, make sure you tell me in which way you want to build this store and it would be nice if you could show some prev work. Make sure you check this notes for futures updates.