As you know the stoves were for my wedding which went really well and the chefs really admires your stoves. Since then I have been on honeymoon and have only just returned. To answer your questions, I cannot remember exactly the cost of the duty but from memory it was about £30 ($45). This is for the four stoves I bought which were in one parcel. I am not sure if you would need to pay the same for just one stove or a quarter the amount. I suspect it should be worked out on the value of the package and therefore should be a quarter. I did have a problem with the valve connector as it would not fit UK propane cylinders. I found a company called gaslow who managed to provide me with an adaptor which also had the benefit of including a gauge for indicating the gas left in the bottle. This cost about £25 ($38) per stove. You can find a link to their website:
http://www.gaslow.co.uk 