I echo Alison's thoughts - what you pay is what you get - and medical insurance you can't get enough in my book, especially in the States. I am VERY particular about where we get ours from - or rather what it includes. And I don't pay way over the odds either. Perhaps this is because we've travelled to the States many times, the Philippines, Hong Kong and the caribbean where we wanted to make sure we were more than adequately covered for one of those "god forbid, stranded in the middle of nowhere" moments.
Fortunately, one those didn't happen out in the more remote places, but we have had to claim a few times for poor old DD (ear infection one year, croup and emergency admission to ER on our first trip to Florida, high fever . . . .) and never had any problem.
We've been with Nationwide
travel insurance for the past four years and each year they manage to come in with a competitive quote. I look on the net each time we have to renew to see if I can get better and cheaper anywhere, but no where comes close. I would add both my DD and I have prexisting medical conditions (asthma and hypertension) and whilst we don't have to pay any more on anyone's policies (they're both considered ok to cover for, none of our conditions critical), but when you try and get a quote online, because you tick the prexisting box it is a bit of pain to get a quote since you have to phone!
Especially for travel to the US you MUST ensure you have millions of $ in medical cover - the bills for Katie's visits to ER for her ear infection last trip and the croup were horrendous - and they were only "trivial" problems.