As a lefty who received “gifts” from her conservative parents, let me suggest giving the gift separate from a major holiday. Something I wish my parents had done that could work as a gift of sorts for you would be to take your son out for coffee or breakfast. Nothing fancy, preferably not busy. Talk to them about why they think what they do. Don’t combat them, just try to understand. Ask them if they would be comfortable talking more after you’ve had time to think about what they said.
“Hey [child’s name], you know that we have strong beliefs about certain subjects. We feel we have good reasons to believe the things we do, but there are smart people in the world who disagree with us. You are a smart kid, and that is reflected in the way you look for answers to problems that the way you have been brought up to think hasn’t offered a solution for. It would mean the world to your mom and I to know out son better, what are some things you’ve thought deeply about recently?”
There are some alternatives that are usually affiliated with a religion. CHM is one such organization. Members all pay a recurring fee like they do with insurance, and all have access to the pool for their healthcare.
I have never used one so I cant speak to the efficacy, but it seems to answer your question.