Which product did you choose from SeeSawUSA? I am always on the look-out for black-out systems. I have bought some El-Cheapo ones from IKEA (made in Poland, but discontinued). The product seems fine, although I have not installed them yet. They don't have the fancy side tracks, etc.
If the British supplier is not used to shipping overseas, they are probably rather reluctant to quote a shipping price, since the shipping to North America is often quite dear and wide ranging in price. I am located in Canada.