I would love that shipping cost could come from a magento attribute, instead of a fixed amount.

Adding the amount to the price (for example create attribute in magento as an ebay price) doesnt make sense as it will scare buyers off who see an item which sells for say £2 but your listing it at £8 to cover the shipping cost - the buyer does not take into account the shipping fee!

It is clearer to say to the buyer - yes that iron i will sell to you for £2 but understand it costs me £8 to ship it!