Duty from the US is a real pain, because the threshold value is very low (much lower than if you bring the bits yourself in your luggage), and then there's VAT and handling fee on top. The cost price can easily double.
I just got lucky - a bod in the US, big parts dealer, selling an NOS 400F toolkit. With shipping, it cost me just over £50. Got a bid of £100 on it already, and a dozen watchers.