Are there any ways to pay for cryonics or similar, if you don't have (enough) life insurance? Do you think a fundraiser like go fund me could help? Any advice would be appreciated.
While this isn't a solution, you could get associate membership at Alcor. It costs only $60 a year. The advantage (I think) is that you could fill out all the paperwork required to get cryopreserved (this can take a while). Consequently if you get a fatal diagnosis and can raise the needed funds ($80,000 for neurocryopreservation) you could get preserved. https://alcor.org/BecomeMember/associate.html
Often, Cryorus allows post-mortem payment. That is, your relatives will pay from your inheritance.
You might get better responses at New Cryonet or r/cryonics. The cryonics community doesn't seem to be very active here.
It's a tricky question and depends a lot on your circumstances.
First, there are often cheaper options available. For example, CI is cheaper than Alcor. See https://www.reddit.com/r/cryonics/comments/8ymikj/oc_how_much_does_is_cost_to_preserve_a_brain/
If you have a terminal illness and don't have enough money for even cheaper options like CI, you can try to get in touch with the Venturists, who might be able to vouch for your situation and coordinate a fundraiser (they have done this in the past). Their website seems to be down but I think they are still active: https://web.archive.org/web/20170721065012/http://www.venturist.info/
Best of luck. I'm really sorry for your situation. It's a shame that cryonics is ridiculed and stigmatized and as a result the costs are much higher and this kind of situation is so hard to coordinate.