Can Anyone Help?

I want to book a cruise in US Dollars but because I'm a non US
citizen, all of the standard cruise lines etc are asking for £
Sterling. US citizens seem to pay the same number of dollars as we
pay in pounds sterling e.g. $1200 dollars in the US and £1200 in
sterling.

Anyway, does anyone know of a reliable web site to book in US dollars?

Thankyou in advance.