Depends how fancy they go, cheapest way would be nylon ends with steel inserts under the bolts, and a steel or ally tube between them, most expensive would be a CFRP honeycomb sheathed in carbon fibre with stainless steel bolt inserts and carbon tube linking them....but I imagine somewhere between the two.
Basically something like this, where the honeycomb is custom shaped to the strut top dome, so we can make a nice thick, stiff endplate by skinning it carbon or steel as we don't need it to bow down to match the top like the thin steel ones, so it should work out far, far stiffer and being mainly a skin over the core still keeps it light, but I'm just playing with idea's atm:
And you can see what I mean about having the proper shape to the underside:
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