$150k can be a lot for some and not enough for others. DW and I (older than pletal) pay $25K per year for policies that allow us the pleasure of paying the first $10K or so in medical expenses, so I think it is a reasonable question. Worse, if one has a disqualifying pre-condition, no insurance may be available and $150K is too little to self-insure.
Estimating health care costs has 2 components: the current cost of coverage and the rate it will increase. The current cost varies greatly by state so the best way to estimate cost of coverage is by contacting an insurance broker and getting some quotes.
The rate of increase is anybody's guess, but it has been double digit for the past decade. In addition, when you hit age milestones: 50 55, and 60, your premium increases due to age, and each of those could easily be an additional 10%. If you have access to a large group policy and can continue that coverage, you are likely to see lower rates and increases.
If it sounds complicated, it is. But you can still develop a reasonable estimate. Start with the type of policy you would have and work from there.