How long do support posts last? Any reason to be concerned with rust on them? Seem to be working fine.
Obviously rust isn't a good thing. I don't seen enough here for immediate concern, but eventually you'll need to replace them if action isn't taken.
Since they appear to be sitting on the slab, as opposed to being embedded in it, you can easily replace them with screw-type floor jacks. They aren't terribly expensive, and you could use a bottle jack and a wood 4x4 as a temporary post while you do the work.
You might just paint these, though. Use a wire brush to clean away loose material, then apply a suitable primer. Stop there or add a nice top coat. Wait 20 years and repeat.
Some structural steel is designed to allow the outer surface to rust, because it then forms an oxide layer that prevents the more destructive deep rust.