It'll be different for everyone. It should be a function of your current income, your life expectancy, and your current asset value. The higher your income, the more you're worth, the more you're willing to pay. The healthier you are, the further away from death you are, the less you're willing to pay. And vice versa. It's pretty much how insurers decide how much they're willing to insure on your death anyways, and how much premium to charge you to hedge against that risk... you having died instead of lived on to continue earning wages, profiting from investing, collecting interest etc. Weight this potential loss against your life expectancy and continuously increasing probability of death.
I'm not saying my income, asset value, or health on some internet forum, so I guess my answer is half. Whatever I make from salary, investment, interest, blah blah blah everything. I'll give half what I make in a year to live another year, or half what I make a day to live another day. And I'll just assume I'll die immediately with no payment.