Postages costs can be extremely expensive especially if it for delivery of something large or heavy. When looking to buy anything online which will require postage, always check to find out the delivery price. Often products are advertised at a reasonably low price but then the postage charges are extremely high meaning overall you pay more than you should.
Some companies will offer combined postage if you are buying multiple items from them, but be sure to check this prior to placing your order as often this needs to be done before committing to buy.
If you are buying through an auction site such as eBay, then it is vital to check the delivery details. It may be that the person selling the item has listed it as collection only or that you are required to sort out your own courier for delivery. If the postage seems high, you could obtain your own quote from a courier and often to arrange the delivery yourself.