Not sure how much the people you talk to about this care about facts supporting the argument but if they do, the US government spends by far the highest %gdp on healthcare out of any country in the world (https://ourworldindata.org/grapher/public-health-expenditure-share-gdp?tab=table), and people still go bankrupt from medical debt.

Now, in reality this figure is likely a bit skewed because well earning jobs (like doctors) in the US make obscene amounts of money (hello extremely high income inequality), but you don’t have to tell them that, and also the other argument still applies anyway.

To add something else, preventative care can often save costs compared to the ailments it’s trying to prevent. By making preventative care free, more people are likely to get it, reducing overall healthcare costs.