Pre-Order - price calculation - payment

I want to support such a workflow that customer pre-order some custom product (ex. t-shiths with it's own design, color and so on). I created my own custom payment plugin and modify checkout code that when the product is pre-ordered so I push step to go toward my payment which is only changing order and payment status.
But I have no idea how to make next step means:
- after checking pre-order content I want to be able to set calculated price for order (manually set it in the order detail page)
- but when the price is set I want to give the order for customer to pay - the best way is (maybe) put the order again for shippment and payment process so the customer can pay using set it payment methods and finish order.

Do You have any idea how to make it ?

May I push order to the client cart and to the order process again ?

Until the customer "confirm"s the order, the Order record does not exist  (only ShoppingCartItem records exist prior to Order being created.)  So, you'll need to work out some other way to have customer select a payment method.

What  public ActionResult RePostPayment(int orderId) - this method can do for me ?
It's defined in the OrderController.
Maybe I can change order price and push order again to the payment ?