A couple of years ago I was quoted just under £2,000 for a fortnight in Spain!! Mainly because my cancer was not one of those listed by the insurance companies - although I was in remission and could provide results of a scan to prove it. It was even suggested I call it cancer of the appendix because it had been found in that area. When I challenged this, saying what if I needed to claim, wouldn't the insurance company be within their rights to disallow the claim? The response - oh well, yes I suppose so!!
I then found a company called Waltham Travel, who agreed to insure me for £39 but this would exclude all pre-existing medical conditions. As it happens, I didn't actually go to Spain in the end for a number of reasons, but Waltham Travel couldn't have been more helpful. If they are still available then I would suggest they are well worth a try.