None of the classic series Rainsongs have truss rods, but their other model lines do have truss rods. Carbon fiber is pretty much bullet proof if it is laid up properly. From what I have seen of them you could hold up a building with a Rainsong neck so the lack of a truss rod would not really bother me much. They do seem to be utterly indifferent to weather, temperature, humidty....
Street prices for most new Rainsong models (e.g. WS1000) are typically a bit lower than a new HD-28, but not by a lot. There are exceptions too, their concert and hybrid models are pretty stoutly priced.
But if you're looking for the Martin D-28 sound you may not like the Rainsong sound and vice versa. They have very different tonal characteristics. The Rainsongs tend to feel and play more like electric guitars. Personally, I like them both, but I own a Martin and not a Rainsong.