Ok, this is really simple and it can save you lots of money, pay attention!
Simply click the Buy It Now button on every iPosters item that you want to buy. When you have finished shopping you can then click the Pay Now button on any one of the items.Clicking the pay now nutton will take you to the checkout where all of your items will be included on one order. You will only pay shipping for one poster/print.
You can select almost any payment type at the checkout. If you have a paypal account then it is a 2 click process. Easy!