Drummerdave, lots of folks wear some of the dirtbike type armor commonly called "pressure suits" in the winter under a waterproof shell. These are more than "scatter sheilds" or "roost gaurds"; they are full on certified armor. Thor, Acerbis (ah-chair-bees which is Italian), and many others make them. All have good chest and spine protection. Most also have shoulder and elbow armor. Some you can remove the shoulder and elbow and just wear the chest/back armor (like the Acerbis Cosmo). Acerbis also has the Koerta which is a long sleeved that does not come apart like the Cosmo. They used to have a short sleeved version of the koerta but no longer make it (but see my next paragraph below..). My wife and I have tekrider tekvests for the winter, but in the summer, I wear the Acerbis Cosmo and she the Acerbis Koerta. I have an extra Koerta that I keep around to borrow out as well. Any of these, or other brands, would make a economical armor setup. You can also find these used and find tekvests used so watch for those on your local craigslist, on this forum, ebay, etc.
Shameless plug, I have a short sleeved Acerbis Koerta new in the bag that I'm going to list for sale. Just need to find the time to see what they are going for nowadays before I list it. They used to be over $100 but I think they are going for a fair bit less even brand new. These have the chest and back armor only and not shoulder or elbow armor and fit under shells well. As far as our other three Acerbis sets, we'll continue to use them for summer as we have for 5 or 6 years now. We love them.