You just don't get any healthcare. There are some free and low cost options, but you usually have to demonstrate significant need. I know I was looking to access free or subsidised healthcare and I had to prove that my income from the previous tax year was below a certain threshold. But my previous year's income was fine, because I was employed (and had health insurance!). In was right then and there where I could not afford healthcare, because I'd been made redundant and had no health insurance.
I had a situation just before I lost my job where I'd had a smear done. The results were abnormal, but there had been a mix up and they'd given me someone else's results (normal). Then a month later, called to say actually there had been a mistake and I needed a colposcopy and biopsy. But in that month, I'd lost my health insurance. I tried to have the colposcopy done at planned parenthood or another sort of charity that offered low cost women's health care. But even then the colposcopy was $1000! I couldn't afford that being unemployed and then even when I was employed again, I had no health insurance as my employer didn't offer it. I waited 2 years while I may have possibly had cervical cancer until I had insurance again and could afford the colposcopy. In the end, the damn thing still cost me $600 with my expensive health insurance - which if I'd known, I would have taken out a loan to try to afford it years before!
Thankfully, the biopsy was okay and the cells were abnormal, but not cancerous. I was very lucky. There are many people are not so lucky. Dh had a friend when we lived in the US who lost his house to pay for his cancer treatment. It cost $200,000. He had no insurance and the hospital will usually write off some of it, but that was the bit left for him to pay.
No idea what it's like now with the Affordable Care Act and the changes brought in by Obama, because I left as soon as I could get a visa to move to the UK and have never looked back. But back in 2003, I was paying $600 a month for health insurance, plus co-pays for visits and extra for tests (thank god I never needed a hospital stay), and that was just for me. I couldn't imagine how I'd afford that now with a family and all the costs of being an adult. Back then I was like 20 and I had almost no living expenses and everything just went on my car and insurance.