I have, though never for as much as £1800 - most I ever got for a trial was £300, and that was one night in a centre & 3 follow-up appointments over 3 months. Well worth doing in my own experience, but it's all subjective.
Granted, there's a real risk to it, but I don't see it as putting my life on the line for a bit of extra cash, but more that I'm gambling my health against scientific development and the cash is a nice bonus. My own curious mix of narcissism, mysanthropy and altruism resolves any such conflicts into whether the sacrifice of any part of my imspirational existence can benefit the masses of filth I'm forced to wallow in, even if the primary motive is greed and self-fulfillment. I'm just that awesome.