I ended up buying mine from the US, OWC was cheaper than iFixit by a way and they had a discount on the kit which swung it for me.
Also the shipping at iFixit is one choice only and it's much dearer than OWC where I chose the cheapest as I wasn't bothered about the speed of the delivery.
To be honest, if you have all the tools already then just buying the cable is the way to go as they mark up the kits for what is essentially just 4 rubber washers, 4 screws, the motherboard removal tool and a few screwdrivers that are ok but aren't eactly high quality.
The only part that might be awkward to get is the motherboard tool, but even that could be got around with something else like long thin screws or the like.
Last point is that if you don't buy in the US you will avoid the nasty double charge when the item hits customs here, the item incurred a £5 charge which Royal Mail duly paid on my behalf and then added an £8 on top of which is non-negotiable so thats an extra £13.
OWC should really factor a pre-paid customs charge in like Amazon does to stop this happening.