From 1 only child to another, let me tell you that you will not be able to take on that monster. Your main proiority, is your immediate family. Your husband and your children. I had to make the choice for my parents as you now do for yours and I paid for nothing on their behalf. Not because I didn't want to but because I myself did not have it to give. They both had medicaid/medicare and this was what I had to depend on. They both received their checks and we ended up living together. They contributed to my household and I was able to care for them in our home. They never went to a nursing home, but it was there as an option if I needed it, and I was grateful for that. Both my parents lived with me, got ill and went into a hospital. My mom passed on in the hospital. My dad was ill, recooperated at a rehab/nursing home, got ill and passed away in the hospital.
Don't put that extra pressure on yourself to have to care for them in a way that may be too much for you. Yes, you are the only child and its your turn to take care of them, but take care of them with what they have available to them. Perhaps living in the same home is a possibility. If not, whatever the government provides can be an option. Its hard enough to have aging parents, trying to pay for insurance out of your pocket only makes things more difficult for you, your relationship with your husband and everything else. Good luck.