My USA health insurance used to cover the blood test for vitamin D, but stopped about 10 years ago. Now to get a blood test it's somewhere in the $70-100 extra range if I want to get that in addition to a normal yearly physical blood panel.
Yes, that prices isn't that much for your health, but if you decide you want to take a LOT of vitamin D then you need to comprehend the blood test costs.
Yes, everyone should take vitamin D supplements, but too much vitamin D is very dangerous.
Everyone should regularly get tested for their vitamin D level as well. It's cheap. It's easy. It's quick.