Shopping Cart for DHL/UPS-style site?

Hi,

I could be involved in customising a shopping cart for a site not dissimilar to DHL, but a lot smaller.

I was wondering from experience, what everyone feels is the best route to go down, custom-build the cart(costing more obviously) or download software from the net, which could work a little like DHL(weigh package, height, length, breadth and place of delivery, costs etc). Receive payment etc., then collect item.

I know of software like osCommerce and CubeCart etc., but wondered if there are any suited to packaging/delivery companies.

Many thanks,

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