Folks, I know this comes up frequently so thought I'd share my experience.
Background: CLL and Hypertension for me, treated with FCR second half 2012. Plus second person (my wife) with no declared problems. Travelling to USA for 2.5 weeks in November.
Of the companies I checked no-one would do multi-trip (I think because I have two declared issues and USA).
Checked several by phone and web range other than the one I picked was £350-£600. One even dropped the price on the phone from £500 to £450 and seemed to think they were doing me a favour.
Ended up going with World First which was £189.77 including a £62.74 excess for me.
I have no affiliation with World First, other than this one use of them. I did not have to claim so no idea how they would have been in that situation however, they were less invasive than some.
(Updated to make it clearer that the price included the excess - was ambiguous before)