RM does not have control of resalers. If you want someone in the us to order you one and then ship it too you it could come out to be less than 20 pounds, approx 25 dollars would be the whole cost in dollars. 12 to have it shipped to them, and then 13 to ship it to you.
Using international flatrate boxes, from usps.
I live in the UK and have ordered the manual direct from RootsMagic. My credit card has charged me a total of £13.75. Despite the postage ($12) being more than the price of the manual ($10), this is still cheaper than if I bought it in the UK.